Run clang-tidy’s modernize-use-nullptr pass.

This replaces all NULL or 0 with nullptr when assigned to or returned as
a pointer.

45 files changed, 227 insertions, 227 deletions

diff --git a/src/ui/widget/attr-widget.h b/src/ui/widget/attr-widget.h
index e54116a67..8dbff8874 100644
--- a/src/ui/widget/attr-widget.h
+++ b/src/ui/widget/attr-widget.h
@@ -157,7 +157,7 @@ protected:
             const gchar* val = o->getRepr()->attribute(name);
             return val;
         }
-        return 0;
+        return nullptr;
     }
 
 private:
diff --git a/src/ui/widget/clipmaskicon.cpp b/src/ui/widget/clipmaskicon.cpp
index eceff13ca..509e218a9 100644
--- a/src/ui/widget/clipmaskicon.cpp
+++ b/src/ui/widget/clipmaskicon.cpp
@@ -30,9 +30,9 @@ ClipMaskIcon::ClipMaskIcon() :
     _pixMaskName(INKSCAPE_ICON("path-difference")),
     _pixBothName(INKSCAPE_ICON("bitmap-trace")),
     _property_active(*this, "active", 0),
-    _property_pixbuf_clip(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_mask(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_both(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0))
+    _property_pixbuf_clip(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_mask(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_both(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr))
 {
     
     property_mode() = Gtk::CELL_RENDERER_MODE_ACTIVATABLE;
@@ -46,7 +46,7 @@ ClipMaskIcon::ClipMaskIcon() :
     _property_pixbuf_mask = icon_theme->load_icon(_pixMaskName, phys, (Gtk::IconLookupFlags)0);
     _property_pixbuf_both = icon_theme->load_icon(_pixBothName, phys, (Gtk::IconLookupFlags)0);
 
-    property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(0);
+    property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 }
 
 void ClipMaskIcon::get_preferred_height_vfunc(Gtk::Widget& widget,
@@ -97,7 +97,7 @@ void ClipMaskIcon::render_vfunc( const Cairo::RefPtr<Cairo::Context>& cr,
             property_pixbuf() = _property_pixbuf_both;
             break;
         default:
-            property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(0);
+            property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(nullptr);
             break;
     }
     Gtk::CellRendererPixbuf::render_vfunc( cr, widget, background_area, cell_area, flags );
diff --git a/src/ui/widget/color-entry.cpp b/src/ui/widget/color-entry.cpp
index f5658c3a6..b766dc9ed 100644
--- a/src/ui/widget/color-entry.cpp
+++ b/src/ui/widget/color-entry.cpp
@@ -61,7 +61,7 @@ void ColorEntry::on_changed()
     }
 
     gchar *str = g_strdup(text.c_str());
-    gchar *end = 0;
+    gchar *end = nullptr;
     guint64 rgba = g_ascii_strtoull(str, &end, 16);
     if (end != str) {
         ptrdiff_t len = end - str;
diff --git a/src/ui/widget/color-icc-selector.cpp b/src/ui/widget/color-icc-selector.cpp
index c6f5b799f..bd1cfde1b 100644
--- a/src/ui/widget/color-icc-selector.cpp
+++ b/src/ui/widget/color-icc-selector.cpp
@@ -209,21 +209,21 @@ class ComponentUI {
   public:
     ComponentUI()
         : _component()
-        , _adj(0)
-        , _slider(0)
-        , _btn(0)
-        , _label(0)
-        , _map(0)
+        , _adj(nullptr)
+        , _slider(nullptr)
+        , _btn(nullptr)
+        , _label(nullptr)
+        , _map(nullptr)
     {
     }
 
     ComponentUI(colorspace::Component const &component)
         : _component(component)
-        , _adj(0)
-        , _slider(0)
-        , _btn(0)
-        , _label(0)
-        , _map(0)
+        , _adj(nullptr)
+        , _slider(nullptr)
+        , _btn(nullptr)
+        , _label(nullptr)
+        , _map(nullptr)
     {
     }
 
@@ -290,7 +290,7 @@ class ColorICCSelectorImpl {
 const gchar *ColorICCSelector::MODE_NAME = N_("CMS");
 
 ColorICCSelector::ColorICCSelector(SelectedColor &color)
-    : _impl(NULL)
+    : _impl(nullptr)
 {
     _impl = new ColorICCSelectorImpl(this, color);
     init();
@@ -302,7 +302,7 @@ ColorICCSelector::~ColorICCSelector()
 {
     if (_impl) {
         delete _impl;
-        _impl = 0;
+        _impl = nullptr;
     }
 }
 
@@ -314,16 +314,16 @@ ColorICCSelectorImpl::ColorICCSelectorImpl(ColorICCSelector *owner, SelectedColo
     , _updating(FALSE)
     , _dragging(FALSE)
     , _fixupNeeded(0)
-    , _fixupBtn(0)
-    , _profileSel(0)
+    , _fixupBtn(nullptr)
+    , _profileSel(nullptr)
     , _compUI()
-    , _adj(0)
-    , _slider(0)
-    , _sbtn(0)
-    , _label(0)
+    , _adj(nullptr)
+    , _slider(nullptr)
+    , _sbtn(nullptr)
+    , _label(nullptr)
 #if defined(HAVE_LIBLCMS1) || defined(HAVE_LIBLCMS2)
     , _profileName()
-    , _prof(0)
+    , _prof(nullptr)
     , _profChannelCount(0)
     , _profChangedID(0)
 #endif // defined(HAVE_LIBLCMS1) || defined(HAVE_LIBLCMS2)
@@ -332,9 +332,9 @@ ColorICCSelectorImpl::ColorICCSelectorImpl(ColorICCSelector *owner, SelectedColo
 
 ColorICCSelectorImpl::~ColorICCSelectorImpl()
 {
-    _adj = 0;
-    _sbtn = 0;
-    _label = 0;
+    _adj = nullptr;
+    _sbtn = nullptr;
+    _label = nullptr;
 }
 
 void ColorICCSelector::init()
@@ -524,7 +524,7 @@ void ColorICCSelectorImpl::_profileSelected(GtkWidget * /*src*/, gpointer data)
     GtkTreeIter iter;
     if (gtk_combo_box_get_active_iter(GTK_COMBO_BOX(self->_profileSel), &iter)) {
         GtkTreeModel *store = gtk_combo_box_get_model(GTK_COMBO_BOX(self->_profileSel));
-        gchar *name = 0;
+        gchar *name = nullptr;
 
         gtk_tree_model_get(store, &iter, 1, &name, -1);
         self->_switchToProfile(name);
@@ -615,9 +615,9 @@ void ColorICCSelectorImpl::_switchToProfile(gchar const *name)
 #endif // DEBUG_LCMS
         if (tmp.icc) {
             delete tmp.icc;
-            tmp.icc = 0;
+            tmp.icc = nullptr;
             dirty = true;
-            _fixupHit(0, this);
+            _fixupHit(nullptr, this);
         }
         else {
 #ifdef DEBUG_LCMS
@@ -789,7 +789,7 @@ void ColorICCSelectorImpl::_setProfile(SVGICCColor *profile)
         // Need to clear out the prior one
         profChanged = true;
         _profileName.clear();
-        _prof = 0;
+        _prof = nullptr;
         _profChannelCount = 0;
     }
     else if (profile && !_prof) {
@@ -855,7 +855,7 @@ void ColorICCSelectorImpl::_setProfile(SVGICCColor *profile)
         }
         else {
             // Give up for now on named colors
-            _prof = 0;
+            _prof = nullptr;
         }
     }
 
diff --git a/src/ui/widget/color-notebook.cpp b/src/ui/widget/color-notebook.cpp
index 308bb968e..5b0f12e51 100644
--- a/src/ui/widget/color-notebook.cpp
+++ b/src/ui/widget/color-notebook.cpp
@@ -88,7 +88,7 @@ ColorNotebook::~ColorNotebook()
 {
     if (_buttons) {
         delete[] _buttons;
-        _buttons = 0;
+        _buttons = nullptr;
     }
 }
 
@@ -271,7 +271,7 @@ void ColorNotebook::_updateICCButtons()
 
 #if defined(HAVE_LIBLCMS1) || defined(HAVE_LIBLCMS2)
     /* update color management icon*/
-    gtk_widget_set_sensitive(_box_colormanaged, color.icc != NULL);
+    gtk_widget_set_sensitive(_box_colormanaged, color.icc != nullptr);
 
     /* update out-of-gamut icon */
     gtk_widget_set_sensitive(_box_outofgamut, false);
@@ -330,7 +330,7 @@ void ColorNotebook::_addPage(Page &page)
         tab_label->set_name("ColorModeLabel");
         gint page_num = gtk_notebook_append_page(GTK_NOTEBOOK(_book), selector_widget->gobj(), tab_label->gobj());
 
-        _buttons[page_num] = gtk_radio_button_new_with_label(NULL, mode_name.c_str());
+        _buttons[page_num] = gtk_radio_button_new_with_label(nullptr, mode_name.c_str());
         gtk_widget_set_name(_buttons[page_num], "ColorModeButton");
         gtk_toggle_button_set_mode(GTK_TOGGLE_BUTTON(_buttons[page_num]), FALSE);
         if (page_num > 0) {
diff --git a/src/ui/widget/color-scales.cpp b/src/ui/widget/color-scales.cpp
index cb6349c4b..620e77cbf 100644
--- a/src/ui/widget/color-scales.cpp
+++ b/src/ui/widget/color-scales.cpp
@@ -51,10 +51,10 @@ ColorScales::ColorScales(SelectedColor &color, SPColorScalesMode mode)
     , _mode(SP_COLOR_SCALES_MODE_NONE)
 {
     for (gint i = 0; i < 5; i++) {
-        _l[i] = 0;
-        _a[i] = 0;
-        _s[i] = 0;
-        _b[i] = 0;
+        _l[i] = nullptr;
+        _a[i] = nullptr;
+        _s[i] = nullptr;
+        _b[i] = nullptr;
     }
 
     _initUI(mode);
@@ -66,10 +66,10 @@ ColorScales::ColorScales(SelectedColor &color, SPColorScalesMode mode)
 ColorScales::~ColorScales()
 {
     for (gint i = 0; i < 5; i++) {
-        _l[i] = 0;
-        _a[i] = 0;
-        _s[i] = 0;
-        _b[i] = 0;
+        _l[i] = nullptr;
+        _a[i] = nullptr;
+        _s[i] = nullptr;
+        _b[i] = nullptr;
     }
 }
 
@@ -283,7 +283,7 @@ void ColorScales::on_show()
 
 void ColorScales::_getRgbaFloatv(gfloat *rgba)
 {
-    g_return_if_fail(rgba != NULL);
+    g_return_if_fail(rgba != nullptr);
 
     switch (_mode) {
         case SP_COLOR_SCALES_MODE_RGB:
@@ -314,7 +314,7 @@ void ColorScales::_getCmykaFloatv(gfloat *cmyka)
 {
     gfloat rgb[3];
 
-    g_return_if_fail(cmyka != NULL);
+    g_return_if_fail(cmyka != nullptr);
 
     switch (_mode) {
         case SP_COLOR_SCALES_MODE_RGB:
@@ -384,7 +384,7 @@ void ColorScales::setMode(SPColorScalesMode mode)
             gtk_label_set_markup_with_mnemonic(GTK_LABEL(_l[3]), _("_A:"));
             _s[3]->set_tooltip_text(_("Alpha (opacity)"));
             gtk_widget_set_tooltip_text(_b[3], _("Alpha (opacity)"));
-            _s[0]->setMap(NULL);
+            _s[0]->setMap(nullptr);
             gtk_widget_hide(_l[4]);
             _s[4]->hide();
             gtk_widget_hide(_b[4]);
@@ -485,7 +485,7 @@ void ColorScales::setMode(SPColorScalesMode mode)
             gtk_label_set_markup_with_mnemonic(GTK_LABEL(_l[4]), _("_A:"));
             _s[4]->set_tooltip_text(_("Alpha (opacity)"));
             gtk_widget_set_tooltip_text(_b[4], _("Alpha (opacity)"));
-            _s[0]->setMap(NULL);
+            _s[0]->setMap(nullptr);
             gtk_widget_show(_l[4]);
             _s[4]->show();
             gtk_widget_show(_b[4]);
@@ -704,7 +704,7 @@ void ColorScales::_updateSliders(guint channels)
 
 static const gchar *sp_color_scales_hue_map(void)
 {
-    static gchar *map = NULL;
+    static gchar *map = nullptr;
 
     if (!map) {
         gchar *p;
diff --git a/src/ui/widget/color-slider.cpp b/src/ui/widget/color-slider.cpp
index ed034598e..58a236e92 100644
--- a/src/ui/widget/color-slider.cpp
+++ b/src/ui/widget/color-slider.cpp
@@ -42,7 +42,7 @@ ColorSlider::ColorSlider(Glib::RefPtr<Gtk::Adjustment> adjustment)
     , _value(0.0)
     , _oldvalue(0.0)
     , _mapsize(0)
-    , _map(NULL)
+    , _map(nullptr)
 {
     _c0[0] = 0x00;
     _c0[1] = 0x00;
@@ -170,10 +170,10 @@ bool ColorSlider::on_button_press_event(GdkEventButton *event)
                       window,
                       GDK_SEAT_CAPABILITY_ALL_POINTING,
                       FALSE,
-                      NULL,
+                      nullptr,
                       reinterpret_cast<GdkEvent *>(event),
-                      NULL,
-                      NULL);
+                      nullptr,
+                      nullptr);
 #else
 	auto device = gdk_event_get_device(reinterpret_cast<GdkEvent *>(event));
         gdk_device_grab(device,
@@ -286,7 +286,7 @@ void ColorSlider::_onAdjustmentValueChanged()
 void ColorSlider::setColors(guint32 start, guint32 mid, guint32 end)
 {
     // Remove any map, if set
-    _map = 0;
+    _map = nullptr;
 
     _c0[0] = start >> 24;
     _c0[1] = (start >> 16) & 0xff;
@@ -354,7 +354,7 @@ bool ColorSlider::on_draw(const Cairo::RefPtr<Cairo::Context> &cr)
         const guchar *b =
             sp_color_slider_render_map(0, 0, carea.get_width(), carea.get_height(), _map, s, d, _b0, _b1, _bmask);
 
-        if (b != NULL && carea.get_width() > 0) {
+        if (b != nullptr && carea.get_width() > 0) {
             Glib::RefPtr<Gdk::Pixbuf> pb = Gdk::Pixbuf::create_from_data(
                 b, Gdk::COLORSPACE_RGB, false, 8, carea.get_width(), carea.get_height(), carea.get_width() * 3);
 
@@ -377,7 +377,7 @@ bool ColorSlider::on_draw(const Cairo::RefPtr<Cairo::Context> &cr)
             const guchar *b = sp_color_slider_render_gradient(0, 0, wi, carea.get_height(), c, dc, _b0, _b1, _bmask);
 
             /* Draw pixelstore 1 */
-            if (b != NULL && wi > 0) {
+            if (b != nullptr && wi > 0) {
                 Glib::RefPtr<Gdk::Pixbuf> pb =
                     Gdk::Pixbuf::create_from_data(b, Gdk::COLORSPACE_RGB, false, 8, wi, carea.get_height(), wi * 3);
 
@@ -397,7 +397,7 @@ bool ColorSlider::on_draw(const Cairo::RefPtr<Cairo::Context> &cr)
                                                               _b0, _b1, _bmask);
 
             /* Draw pixelstore 2 */
-            if (b != NULL && wi > 0) {
+            if (b != nullptr && wi > 0) {
                 Glib::RefPtr<Gdk::Pixbuf> pb =
                     Gdk::Pixbuf::create_from_data(b, Gdk::COLORSPACE_RGB, false, 8, wi, carea.get_height(), wi * 3);
 
@@ -448,7 +448,7 @@ bool ColorSlider::on_draw(const Cairo::RefPtr<Cairo::Context> &cr)
 static const guchar *sp_color_slider_render_gradient(gint x0, gint y0, gint width, gint height, gint c[], gint dc[],
                                                      guint b0, guint b1, guint mask)
 {
-    static guchar *buf = NULL;
+    static guchar *buf = nullptr;
     static gint bs = 0;
     guchar *dp;
     gint x, y;
@@ -456,7 +456,7 @@ static const guchar *sp_color_slider_render_gradient(gint x0, gint y0, gint widt
 
     if (buf && (bs < width * height)) {
         g_free(buf);
-        buf = NULL;
+        buf = nullptr;
     }
     if (!buf) {
         buf = g_new(guchar, width * height * 3);
@@ -503,14 +503,14 @@ static const guchar *sp_color_slider_render_gradient(gint x0, gint y0, gint widt
 static const guchar *sp_color_slider_render_map(gint x0, gint y0, gint width, gint height, guchar *map, gint start,
                                                 gint step, guint b0, guint b1, guint mask)
 {
-    static guchar *buf = NULL;
+    static guchar *buf = nullptr;
     static gint bs = 0;
     guchar *dp;
     gint x, y;
 
     if (buf && (bs < width * height)) {
         g_free(buf);
-        buf = NULL;
+        buf = nullptr;
     }
     if (!buf) {
         buf = g_new(guchar, width * height * 3);
diff --git a/src/ui/widget/color-wheel-selector.cpp b/src/ui/widget/color-wheel-selector.cpp
index ffdf173ba..b4b6e6e5c 100644
--- a/src/ui/widget/color-wheel-selector.cpp
+++ b/src/ui/widget/color-wheel-selector.cpp
@@ -28,8 +28,8 @@ ColorWheelSelector::ColorWheelSelector(SelectedColor &color)
     : Gtk::Grid()
     , _color(color)
     , _updating(false)
-    , _wheel(0)
-    , _slider(0)
+    , _wheel(nullptr)
+    , _slider(nullptr)
 {
     set_name("ColorWheelSelector");
 
@@ -40,7 +40,7 @@ ColorWheelSelector::ColorWheelSelector(SelectedColor &color)
 
 ColorWheelSelector::~ColorWheelSelector()
 {
-    _wheel = 0;
+    _wheel = nullptr;
 
     _color_changed_connection.disconnect();
     _color_dragged_connection.disconnect();
diff --git a/src/ui/widget/combo-enums.h b/src/ui/widget/combo-enums.h
index 6b69533d2..e06f5b610 100644
--- a/src/ui/widget/combo-enums.h
+++ b/src/ui/widget/combo-enums.h
@@ -114,7 +114,7 @@ public:
         Gtk::TreeModel::iterator i = this->get_active();
         if(i)
             return (*i)[_columns.data];
-        return 0;
+        return nullptr;
     }
 
     void add_row(const Glib::ustring& s)
diff --git a/src/ui/widget/dock-item.cpp b/src/ui/widget/dock-item.cpp
index 29f22977a..7cd841d88 100644
--- a/src/ui/widget/dock-item.cpp
+++ b/src/ui/widget/dock-item.cpp
@@ -25,11 +25,11 @@ DockItem::DockItem(Dock& dock, const Glib::ustring& name, const Glib::ustring& l
     _dock(dock),
     _prev_state(state),
     _prev_position(0),
-    _window(0),
+    _window(nullptr),
     _x(0),
     _y(0),
     _grab_focus_on_realize(false),
-    _gdl_dock_item(0)
+    _gdl_dock_item(nullptr)
 {
     Inkscape::Preferences *prefs = Inkscape::Preferences::get();
     GdlDockItemBehavior gdl_dock_behavior =
@@ -437,8 +437,8 @@ DockItem::getWindow()
 {
     g_return_val_if_fail(_gdl_dock_item, 0);
     Gtk::Container *parent = getWidget().get_parent();
-    parent = (parent ? parent->get_parent() : 0);
-    return (parent ? dynamic_cast<Gtk::Window *>(parent) : 0);
+    parent = (parent ? parent->get_parent() : nullptr);
+    return (parent ? dynamic_cast<Gtk::Window *>(parent) : nullptr);
 }
 
 const Glib::SignalProxyInfo
diff --git a/src/ui/widget/dock.cpp b/src/ui/widget/dock.cpp
index 9c1f0f783..7e90017e8 100644
--- a/src/ui/widget/dock.cpp
+++ b/src/ui/widget/dock.cpp
@@ -27,7 +27,7 @@ namespace {
 
 void hideCallback(GObject * /*object*/, gpointer dock_ptr)
 {
-    g_return_if_fail( dock_ptr != NULL );
+    g_return_if_fail( dock_ptr != nullptr );
 
     Dock *dock = static_cast<Dock *>(dock_ptr);
     dock->hide();
@@ -35,7 +35,7 @@ void hideCallback(GObject * /*object*/, gpointer dock_ptr)
 
 void unhideCallback(GObject * /*object*/, gpointer dock_ptr)
 {
-    g_return_if_fail( dock_ptr != NULL );
+    g_return_if_fail( dock_ptr != nullptr );
 
     Dock *dock = static_cast<Dock *>(dock_ptr);
     dock->show();
@@ -89,7 +89,7 @@ Dock::Dock(Gtk::Orientation orientation)
         static_cast<GdlSwitcherStyle>(prefs->getIntLimited("/options/dock/switcherstyle",
                                                                       GDL_SWITCHER_STYLE_BOTH, 0, 4));
 
-    GdlDockMaster* master = NULL;
+    GdlDockMaster* master = nullptr;
     
     g_object_get(GDL_DOCK_OBJECT(_gdl_dock),
             "master", &master,
@@ -139,7 +139,7 @@ Gtk::Paned *Dock::getParentPaned()
 {
     g_return_val_if_fail(_dock_box, 0);
     Gtk::Container *parent = getWidget().get_parent();
-    return (parent != 0 ? dynamic_cast<Gtk::Paned *>(parent) : 0);
+    return (parent != nullptr ? dynamic_cast<Gtk::Paned *>(parent) : nullptr);
 }
 
 
diff --git a/src/ui/widget/entity-entry.cpp b/src/ui/widget/entity-entry.cpp
index 67412b1e0..48597842b 100644
--- a/src/ui/widget/entity-entry.cpp
+++ b/src/ui/widget/entity-entry.cpp
@@ -45,7 +45,7 @@ EntityEntry*
 EntityEntry::create (rdf_work_entity_t* ent, Registry& wr)
 {
     g_assert (ent);
-    EntityEntry* obj = 0;
+    EntityEntry* obj = nullptr;
     switch (ent->format)
     {
         case RDF_FORMAT_LINE: 
@@ -65,7 +65,7 @@ EntityEntry::create (rdf_work_entity_t* ent, Registry& wr)
 
 EntityEntry::EntityEntry (rdf_work_entity_t* ent, Registry& wr)
     : _label(Glib::ustring(_(ent->title)), Gtk::ALIGN_END),
-      _packable(0),
+      _packable(nullptr),
       _entity(ent), _wr(&wr)
 {
 }
diff --git a/src/ui/widget/font-button.cpp b/src/ui/widget/font-button.cpp
index ed57c803a..1137c2d95 100644
--- a/src/ui/widget/font-button.cpp
+++ b/src/ui/widget/font-button.cpp
@@ -27,20 +27,20 @@ FontButton::FontButton(Glib::ustring const &label, Glib::ustring const &tooltip,
 
 Glib::ustring FontButton::getValue() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<Gtk::FontButton*>(_widget)->get_font_name();
 }
 
 
 void FontButton::setValue (Glib::ustring fontspec)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     static_cast<Gtk::FontButton*>(_widget)->set_font_name(fontspec);
 }
 
 Glib::SignalProxy0<void> FontButton::signal_font_value_changed()
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<Gtk::FontButton*>(_widget)->signal_font_set();
 }
 
diff --git a/src/ui/widget/font-selector-toolbar.cpp b/src/ui/widget/font-selector-toolbar.cpp
index 87dadf211..276b05cd8 100644
--- a/src/ui/widget/font-selector-toolbar.cpp
+++ b/src/ui/widget/font-selector-toolbar.cpp
@@ -263,7 +263,7 @@ FontSelectorToolbar::on_key_press_event (GdkEventKey* key_event)
     gdk_keymap_translate_keyboard_state( Gdk::Display::get_default()->get_keymap(),
                                          key_event->hardware_keycode,
                                          (GdkModifierType)key_event->state,
-                                         0, &key, 0, 0, 0 );
+                                         0, &key, nullptr, nullptr, nullptr );
 
     switch ( key ) {
 
diff --git a/src/ui/widget/imageicon.cpp b/src/ui/widget/imageicon.cpp
index 8e7df7a68..5837c0842 100644
--- a/src/ui/widget/imageicon.cpp
+++ b/src/ui/widget/imageicon.cpp
@@ -86,8 +86,8 @@ void ImageIcon::init()
     //  \FIXME Why?
     if (!Inkscape::Application::exists())
         Inkscape::Application::create("", false);
-    document = NULL;
-    viewerGtkmm = NULL;
+    document = nullptr;
+    viewerGtkmm = nullptr;
     //set_size_request(150,150);
     showingBrokenImage = false;
 }
diff --git a/src/ui/widget/imagetoggler.cpp b/src/ui/widget/imagetoggler.cpp
index 38c84ca51..1200144f1 100644
--- a/src/ui/widget/imagetoggler.cpp
+++ b/src/ui/widget/imagetoggler.cpp
@@ -29,8 +29,8 @@ ImageToggler::ImageToggler( char const* on, char const* off) :
     _pixOffName(off),
     _property_active(*this, "active", false),
     _property_activatable(*this, "activatable", true),
-    _property_pixbuf_on(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_off(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(0))
+    _property_pixbuf_on(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_off(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(nullptr))
 {
     property_mode() = Gtk::CELL_RENDERER_MODE_ACTIVATABLE;
 
diff --git a/src/ui/widget/insertordericon.cpp b/src/ui/widget/insertordericon.cpp
index 5d1f64a54..d402aca37 100644
--- a/src/ui/widget/insertordericon.cpp
+++ b/src/ui/widget/insertordericon.cpp
@@ -25,8 +25,8 @@ InsertOrderIcon::InsertOrderIcon() :
     _pixTopName(INKSCAPE_ICON("insert-top")),
     _pixBottomName(INKSCAPE_ICON("insert-bottom")),
     _property_active(*this, "active", 0),
-    _property_pixbuf_top(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_bottom(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0))
+    _property_pixbuf_top(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_bottom(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr))
 {
     
     property_mode() = Gtk::CELL_RENDERER_MODE_ACTIVATABLE;
@@ -39,7 +39,7 @@ InsertOrderIcon::InsertOrderIcon() :
     _property_pixbuf_top = icon_theme->load_icon(_pixTopName, phys, (Gtk::IconLookupFlags)0);
     _property_pixbuf_bottom = icon_theme->load_icon(_pixBottomName, phys, (Gtk::IconLookupFlags)0);
 
-    property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(0);
+    property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 }
 
 
@@ -88,7 +88,7 @@ void InsertOrderIcon::render_vfunc( const Cairo::RefPtr<Cairo::Context>& cr,
             property_pixbuf() = _property_pixbuf_bottom;
             break;
         default:
-            property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(0);
+            property_pixbuf() = Glib::RefPtr<Gdk::Pixbuf>(nullptr);
             break;
     }
     Gtk::CellRendererPixbuf::render_vfunc( cr, widget, background_area, cell_area, flags );
diff --git a/src/ui/widget/labelled.cpp b/src/ui/widget/labelled.cpp
index 003b64d53..2e9840035 100644
--- a/src/ui/widget/labelled.cpp
+++ b/src/ui/widget/labelled.cpp
@@ -30,7 +30,7 @@ Labelled::Labelled(Glib::ustring const &label, Glib::ustring const &tooltip,
       _label(new Gtk::Label(label, Gtk::ALIGN_END, Gtk::ALIGN_CENTER, mnemonic)),
       _suffix(new Gtk::Label(suffix, Gtk::ALIGN_START))
 {
-    g_assert(g_utf8_validate(icon.c_str(), -1, NULL));
+    g_assert(g_utf8_validate(icon.c_str(), -1, nullptr));
     if (icon != "") {
         _icon = Gtk::manage(new Gtk::Image());
         _icon->set_from_icon_name(icon, Gtk::ICON_SIZE_LARGE_TOOLBAR);
diff --git a/src/ui/widget/layer-selector.cpp b/src/ui/widget/layer-selector.cpp
index e0a52a868..b86222404 100644
--- a/src/ui/widget/layer-selector.cpp
+++ b/src/ui/widget/layer-selector.cpp
@@ -42,7 +42,7 @@ namespace {
 class AlternateIcons : public Gtk::HBox {
 public:
     AlternateIcons(Gtk::IconSize size, Glib::ustring const &a, Glib::ustring const &b)
-    : _a(NULL), _b(NULL)
+    : _a(nullptr), _b(nullptr)
     {
         set_name("AlternateIcons");
         if (!a.empty()) {
@@ -94,7 +94,7 @@ private:
  *  selector is changed.
  */
 LayerSelector::LayerSelector(SPDesktop *desktop)
-: _desktop(NULL), _layer(NULL)
+: _desktop(nullptr), _layer(nullptr)
 {
     set_name("LayerSelector");
     AlternateIcons *label;
@@ -159,7 +159,7 @@ LayerSelector::LayerSelector(SPDesktop *desktop)
 /**  Destructor - disconnects signal handler
  */
 LayerSelector::~LayerSelector() {
-    setDesktop(NULL);
+    setDesktop(nullptr);
     _selection_changed_connection.disconnect();
 }
 
@@ -258,8 +258,8 @@ void LayerSelector::_selectLayer(SPObject *layer) {
     SPObject *root=_desktop->currentRoot();
 
     if (_layer) {
-        sp_object_unref(_layer, NULL);
-        _layer = NULL;
+        sp_object_unref(_layer, nullptr);
+        _layer = nullptr;
     }
 
     if (layer) {
@@ -282,7 +282,7 @@ void LayerSelector::_selectLayer(SPObject *layer) {
         }
 
         _layer = layer;
-        sp_object_ref(_layer, NULL);
+        sp_object_ref(_layer, nullptr);
     }
 
     if ( !layer || layer == root ) {
@@ -353,7 +353,7 @@ void LayerSelector::_buildSiblingEntries(
 
     auto siblings = parent.children | boost::adaptors::filtered(is_layer(_desktop)) | boost::adaptors::reversed;
 
-    SPObject *layer( hierarchy ? &*hierarchy : NULL );
+    SPObject *layer( hierarchy ? &*hierarchy : nullptr );
 
     for (auto& sib: siblings) {
         _buildEntry(depth, sib);
@@ -435,7 +435,7 @@ void LayerSelector::_protectUpdate(sigc::slot<void> slot) {
     _lock_toggled_connection.block(true);
     slot();
 
-    SPObject *layer = _desktop ? _desktop->currentLayer() : 0;
+    SPObject *layer = _desktop ? _desktop->currentLayer() : nullptr;
     if ( layer ) {
         bool wantedValue = ( SP_IS_ITEM(layer) ? SP_ITEM(layer)->isLocked() : false );
         if ( _lock_toggle.get_active() != wantedValue ) {
@@ -480,18 +480,18 @@ void LayerSelector::_buildEntry(unsigned depth, SPObject &object) {
             &node_added,
             &node_removed,
             &attribute_changed,
-            NULL,
+            nullptr,
             &node_reordered
         };
 
         vector = new Inkscape::XML::NodeEventVector(events);
     } else {
         Inkscape::XML::NodeEventVector events = {
-            NULL,
-            NULL,
+            nullptr,
+            nullptr,
             &attribute_changed,
-            NULL,
-            NULL
+            nullptr,
+            nullptr
         };
 
         vector = new Inkscape::XML::NodeEventVector(events);
@@ -501,7 +501,7 @@ void LayerSelector::_buildEntry(unsigned depth, SPObject &object) {
 
     row->set_value(_model_columns.depth, depth);
 
-    sp_object_ref(&object, NULL);
+    sp_object_ref(&object, nullptr);
     row->set_value(_model_columns.object, &object);
 
     Inkscape::GC::anchor(object.getRepr());
@@ -519,7 +519,7 @@ void LayerSelector::_destroyEntry(Gtk::ListStore::iterator const &row) {
     Callbacks *callbacks=reinterpret_cast<Callbacks *>(row->get_value(_model_columns.callbacks));
     SPObject *object=row->get_value(_model_columns.object);
     if (object) {
-        sp_object_unref(object, NULL);
+        sp_object_unref(object, nullptr);
     }
     Inkscape::XML::Node *repr=row->get_value(_model_columns.repr);
     if (repr) {
@@ -543,8 +543,8 @@ void LayerSelector::_prepareLabelRenderer(
     //       "invent" an iterator with null data and try to render it;
     //       where does it come from, and how can we avoid it?
     if ( object && object->getRepr() ) {
-        SPObject *layer=( _desktop ? _desktop->currentLayer() : NULL );
-        SPObject *root=( _desktop ? _desktop->currentRoot() : NULL );
+        SPObject *layer=( _desktop ? _desktop->currentLayer() : nullptr );
+        SPObject *root=( _desktop ? _desktop->currentRoot() : nullptr );
 
         bool isancestor = !( (layer && (object->parent == layer->parent)) || ((layer == root) && (object->parent == root)));
 
diff --git a/src/ui/widget/layer-selector.h b/src/ui/widget/layer-selector.h
index 0b531231a..bcdc2548e 100644
--- a/src/ui/widget/layer-selector.h
+++ b/src/ui/widget/layer-selector.h
@@ -38,7 +38,7 @@ class DocumentTreeModel;
 
 class LayerSelector : public Gtk::HBox {
 public:
-    LayerSelector(SPDesktop *desktop = NULL);
+    LayerSelector(SPDesktop *desktop = nullptr);
     ~LayerSelector() override;
 
     SPDesktop *desktop() { return _desktop; }
diff --git a/src/ui/widget/layertypeicon.cpp b/src/ui/widget/layertypeicon.cpp
index 3a8ffab44..278bd317b 100644
--- a/src/ui/widget/layertypeicon.cpp
+++ b/src/ui/widget/layertypeicon.cpp
@@ -30,9 +30,9 @@ LayerTypeIcon::LayerTypeIcon() :
     _pixPathName(INKSCAPE_ICON("layer-rename")),
     _property_active(*this, "active", false),
     _property_activatable(*this, "activatable", true),
-    _property_pixbuf_layer(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_group(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(0)),
-    _property_pixbuf_path(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(0))
+    _property_pixbuf_layer(*this, "pixbuf_on", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_group(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(nullptr)),
+    _property_pixbuf_path(*this, "pixbuf_off", Glib::RefPtr<Gdk::Pixbuf>(nullptr))
 {
     
     property_mode() = Gtk::CELL_RENDERER_MODE_ACTIVATABLE;
diff --git a/src/ui/widget/licensor.cpp b/src/ui/widget/licensor.cpp
index c9d46bc66..a8325525b 100644
--- a/src/ui/widget/licensor.cpp
+++ b/src/ui/widget/licensor.cpp
@@ -37,10 +37,10 @@ namespace Widget {
 //===================================================
 
 const struct rdf_license_t _proprietary_license = 
-  {_("Proprietary"), "", 0};
+  {_("Proprietary"), "", nullptr};
 
 const struct rdf_license_t _other_license = 
-  {Q_("MetadataLicence|Other"), "", 0};
+  {Q_("MetadataLicence|Other"), "", nullptr};
 
 class LicenseItem : public Gtk::RadioButton {
 public:
@@ -67,7 +67,7 @@ void LicenseItem::on_toggled()
 
     _wr.setUpdating (true);
     SPDocument *doc = SP_ACTIVE_DOCUMENT;
-    rdf_set_license (doc, _lic->details ? _lic : 0);
+    rdf_set_license (doc, _lic->details ? _lic : nullptr);
     if (doc->priv->sensitive) {
         DocumentUndo::done(doc, SP_VERB_NONE, _("Document license updated"));
     }
@@ -80,7 +80,7 @@ void LicenseItem::on_toggled()
 
 Licensor::Licensor()
 : Gtk::VBox(false,4),
-  _eentry (NULL)
+  _eentry (nullptr)
 {
 }
 
@@ -97,7 +97,7 @@ void Licensor::init (Registry& wr)
 
     LicenseItem *i;
     wr.setUpdating (true);
-    i = Gtk::manage (new LicenseItem (&_proprietary_license, _eentry, wr, NULL));
+    i = Gtk::manage (new LicenseItem (&_proprietary_license, _eentry, wr, nullptr));
     Gtk::RadioButtonGroup group = i->get_group();
     add (*i);
     LicenseItem *pd = i;
diff --git a/src/ui/widget/object-composite-settings.cpp b/src/ui/widget/object-composite-settings.cpp
index 3677233bc..fc24ec7cd 100644
--- a/src/ui/widget/object-composite-settings.cpp
+++ b/src/ui/widget/object-composite-settings.cpp
@@ -52,7 +52,7 @@ ObjectCompositeSettings::ObjectCompositeSettings(unsigned int verb_code, char co
 }
 
 ObjectCompositeSettings::~ObjectCompositeSettings() {
-    setSubject(NULL);
+    setSubject(nullptr);
 }
 
 void ObjectCompositeSettings::setSubject(StyleSubject *subject) {
@@ -110,13 +110,13 @@ ObjectCompositeSettings::_blendBlurValueChanged()
 
         SPItem * item = SP_ITEM(*i);
         SPStyle *style = item->style;
-        g_assert(style != NULL);
+        g_assert(style != nullptr);
 
         if (blendmode != "normal") {
             SPFilter *filter = new_filter_simple_from_item(document, item, blendmode.c_str(), radius);
             sp_style_set_property_url(item, "filter", filter, false);
         } else {
-            sp_style_set_property_url(item, "filter", NULL, false);
+            sp_style_set_property_url(item, "filter", nullptr, false);
         }
 
         if (radius == 0 && item->style->filter.set
diff --git a/src/ui/widget/page-sizer.cpp b/src/ui/widget/page-sizer.cpp
index 805333f8e..579049d29 100644
--- a/src/ui/widget/page-sizer.cpp
+++ b/src/ui/widget/page-sizer.cpp
@@ -199,7 +199,7 @@ static PaperSizeRec const inkscape_papers[] = {
      * September 2009 - DAK
      */
 
-    { NULL,                     0,    0, "px" },
+    { nullptr,                     0,    0, "px" },
 };
 
 
@@ -216,7 +216,7 @@ PageSizer::PageSizer(Registry & _wr)
       _dimensionUnits( _("U_nits:"), "units", _wr ),
       _dimensionWidth( _("_Width:"), _("Width of paper"), "width", _dimensionUnits, _wr ),
       _dimensionHeight( _("_Height:"), _("Height of paper"), "height", _dimensionUnits, _wr ),
-      _marginLock( _("Loc_k margins"), _("Lock margins"), "lock-margins", _wr, false, NULL, NULL),
+      _marginLock( _("Loc_k margins"), _("Lock margins"), "lock-margins", _wr, false, nullptr, nullptr),
       _lock_icon(),
       _marginTop( _("T_op margin:"), _("Top margin"), "fit-margin-top", _wr ),
       _marginLeft( _("L_eft:"), _("Left margin"), "fit-margin-left", _wr),
@@ -655,7 +655,7 @@ PageSizer::fire_fit_canvas_to_selection_or_drawing()
     Inkscape::XML::Node *nv_repr;
   
     if ((doc = SP_ACTIVE_DESKTOP->getDocument())
-        && (nv = sp_document_namedview(doc, 0))
+        && (nv = sp_document_namedview(doc, nullptr))
         && (nv_repr = nv->getRepr())) {
         _lockMarginUpdate = true;
         sp_repr_set_svg_double(nv_repr, "fit-margin-top", _marginTop.getValue());
@@ -669,7 +669,7 @@ PageSizer::fire_fit_canvas_to_selection_or_drawing()
     if (verb) {
         SPAction *action = verb->get_action(Inkscape::ActionContext(dt));
         if (action) {
-            sp_action_perform(action, NULL);
+            sp_action_perform(action, nullptr);
         }
     }
 }
diff --git a/src/ui/widget/panel.cpp b/src/ui/widget/panel.cpp
index 281e6e21a..7b54995c1 100644
--- a/src/ui/widget/panel.cpp
+++ b/src/ui/widget/panel.cpp
@@ -45,7 +45,7 @@ Panel::Panel(gchar const *prefs_path, int verb_num) :
     _prefs_path(prefs_path),
     _desktop(SP_ACTIVE_DESKTOP),
     _verb_num(verb_num),
-    _action_area(0)
+    _action_area(nullptr)
 {
     set_name("InkscapePanel");
     set_orientation(Gtk::ORIENTATION_VERTICAL);
diff --git a/src/ui/widget/panel.h b/src/ui/widget/panel.h
index aed90f99c..708d2b957 100644
--- a/src/ui/widget/panel.h
+++ b/src/ui/widget/panel.h
@@ -59,7 +59,7 @@ public:
      * @param prefs_path characteristic path to load/save dialog position.
      * @param verb_num the dialog verb.
      */
-    Panel(gchar const *prefs_path = 0, int verb_num = 0);
+    Panel(gchar const *prefs_path = nullptr, int verb_num = 0);
     ~Panel() override;
 
     gchar const *getPrefsPath() const;
diff --git a/src/ui/widget/preferences-widget.cpp b/src/ui/widget/preferences-widget.cpp
index 078aba9cf..fee392632 100644
--- a/src/ui/widget/preferences-widget.cpp
+++ b/src/ui/widget/preferences-widget.cpp
@@ -351,7 +351,7 @@ draw_text(cairo_t *cr, Geom::Point loc, const char* txt, bool bottom = false,
     pango_font_description_free (font_desc);
 
     PangoRectangle logical_extent;
-    pango_layout_get_pixel_extents(layout, NULL, &logical_extent);
+    pango_layout_get_pixel_extents(layout, nullptr, &logical_extent);
     cairo_move_to(cr, loc[Geom::X], loc[Geom::Y] - (bottom ? logical_extent.height : 0));
     pango_cairo_show_layout(cr, layout);
 }
@@ -732,7 +732,7 @@ void PrefEntryFileButtonHBox::onRelatedEntryChangedCallback()
     }
 }
 
-static Inkscape::UI::Dialog::FileOpenDialog * selectPrefsFileInstance = NULL;
+static Inkscape::UI::Dialog::FileOpenDialog * selectPrefsFileInstance = nullptr;
 
 void PrefEntryFileButtonHBox::onRelatedButtonClickedCallback()
 {
diff --git a/src/ui/widget/preferences-widget.h b/src/ui/widget/preferences-widget.h
index 2b10d1a81..129a7b336 100644
--- a/src/ui/widget/preferences-widget.h
+++ b/src/ui/widget/preferences-widget.h
@@ -274,7 +274,7 @@ class DialogPage : public Gtk::Grid
 {
 public:
     DialogPage();
-    void add_line(bool indent, Glib::ustring const &label, Gtk::Widget& widget, Glib::ustring const &suffix, Glib::ustring const &tip, bool expand = true, Gtk::Widget *other_widget = NULL);
+    void add_line(bool indent, Glib::ustring const &label, Gtk::Widget& widget, Glib::ustring const &suffix, Glib::ustring const &tip, bool expand = true, Gtk::Widget *other_widget = nullptr);
     void add_group_header(Glib::ustring name);
     void set_tip(Gtk::Widget &widget, Glib::ustring const &tip);
 };
diff --git a/src/ui/widget/registered-enums.h b/src/ui/widget/registered-enums.h
index 04ed521cd..c837640d3 100644
--- a/src/ui/widget/registered-enums.h
+++ b/src/ui/widget/registered-enums.h
@@ -32,8 +32,8 @@ public:
                 const Glib::ustring& key,
                 const Util::EnumDataConverter<E>& c,
                 Registry& wr,
-                Inkscape::XML::Node* repr_in = NULL,
-                SPDocument *doc_in = NULL,
+                Inkscape::XML::Node* repr_in = nullptr,
+                SPDocument *doc_in = nullptr,
                 bool sorted = true )
         : RegisteredWidget< LabelledComboBoxEnum<E> >(label, tip, c, (const Glib::ustring &)"", (const Glib::ustring &)"", true, sorted)
     {
diff --git a/src/ui/widget/registered-widget.cpp b/src/ui/widget/registered-widget.cpp
index d539cdcc5..b4c114cff 100644
--- a/src/ui/widget/registered-widget.cpp
+++ b/src/ui/widget/registered-widget.cpp
@@ -207,7 +207,7 @@ RegisteredScalarUnit::~RegisteredScalarUnit()
 
 RegisteredScalarUnit::RegisteredScalarUnit (const Glib::ustring& label, const Glib::ustring& tip, const Glib::ustring& key, const RegisteredUnitMenu &rum, Registry& wr, Inkscape::XML::Node* repr_in, SPDocument *doc_in, RSU_UserUnits user_units)
     : RegisteredWidget<ScalarUnit>(label, tip, UNIT_TYPE_LINEAR, "", "", rum.getUnitMenu()),
-      _um(0)
+      _um(nullptr)
 {
     init_parent(key, wr, repr_in, doc_in);
 
@@ -489,8 +489,8 @@ RegisteredRadioButtonPair::RegisteredRadioButtonPair (const Glib::ustring& label
         const Glib::ustring& tip1, const Glib::ustring& tip2,
         const Glib::ustring& key, Registry& wr, Inkscape::XML::Node* repr_in, SPDocument *doc_in)
     : RegisteredWidget<Gtk::HBox>(),
-      _rb1(NULL),
-      _rb2(NULL)
+      _rb1(nullptr),
+      _rb2(nullptr)
 {
     init_parent(key, wr, repr_in, doc_in);
 
diff --git a/src/ui/widget/registered-widget.h b/src/ui/widget/registered-widget.h
index ca55e5397..bb0f6da8a 100644
--- a/src/ui/widget/registered-widget.h
+++ b/src/ui/widget/registered-widget.h
@@ -135,9 +135,9 @@ protected:
 
 private:
     void construct() {
-        _wr = NULL;
-        repr = NULL;
-        doc = NULL;
+        _wr = nullptr;
+        repr = nullptr;
+        doc = nullptr;
         write_undo = false;
         event_type = 0; //SP_VERB_INVALID
     }
@@ -148,7 +148,7 @@ private:
 class RegisteredCheckButton : public RegisteredWidget<Gtk::CheckButton> {
 public:
     ~RegisteredCheckButton() override;
-    RegisteredCheckButton (const Glib::ustring& label, const Glib::ustring& tip, const Glib::ustring& key, Registry& wr, bool right=true, Inkscape::XML::Node* repr_in=NULL, SPDocument *doc_in=NULL, char const *active_str = "true", char const *inactive_str = "false");
+    RegisteredCheckButton (const Glib::ustring& label, const Glib::ustring& tip, const Glib::ustring& key, Registry& wr, bool right=true, Inkscape::XML::Node* repr_in=nullptr, SPDocument *doc_in=nullptr, char const *active_str = "true", char const *inactive_str = "false");
 
     void setActive (bool);
 
@@ -173,7 +173,7 @@ protected:
 class RegisteredToggleButton : public RegisteredWidget<Gtk::ToggleButton> {
 public:
     ~RegisteredToggleButton() override;
-    RegisteredToggleButton (const Glib::ustring& label, const Glib::ustring& tip, const Glib::ustring& key, Registry& wr, bool right=true, Inkscape::XML::Node* repr_in=NULL, SPDocument *doc_in=NULL, char const *icon_active = "true", char const *icon_inactive = "false");
+    RegisteredToggleButton (const Glib::ustring& label, const Glib::ustring& tip, const Glib::ustring& key, Registry& wr, bool right=true, Inkscape::XML::Node* repr_in=nullptr, SPDocument *doc_in=nullptr, char const *icon_active = "true", char const *icon_inactive = "false");
 
     void setActive (bool);
 
@@ -200,8 +200,8 @@ public:
     RegisteredUnitMenu ( const Glib::ustring& label,
                          const Glib::ustring& key,
                          Registry& wr,
-                         Inkscape::XML::Node* repr_in = NULL,
-                         SPDocument *doc_in = NULL );
+                         Inkscape::XML::Node* repr_in = nullptr,
+                         SPDocument *doc_in = nullptr );
 
     void setUnit (const Glib::ustring);
     Unit const * getUnit() const { return static_cast<UnitMenu*>(_widget)->getUnit(); };
@@ -228,8 +228,8 @@ public:
                            const Glib::ustring& key,
                            const RegisteredUnitMenu &rum,
                            Registry& wr,
-                           Inkscape::XML::Node* repr_in = NULL,
-                           SPDocument *doc_in = NULL,
+                           Inkscape::XML::Node* repr_in = nullptr,
+                           SPDocument *doc_in = nullptr,
                            RSU_UserUnits _user_units = RSU_none );
 
 protected:
@@ -246,8 +246,8 @@ public:
             const Glib::ustring& tip,
             const Glib::ustring& key,
             Registry& wr,
-            Inkscape::XML::Node* repr_in = NULL,
-            SPDocument *doc_in = NULL );
+            Inkscape::XML::Node* repr_in = nullptr,
+            SPDocument *doc_in = nullptr );
 protected:
     sigc::connection _value_changed_connection;
     void on_value_changed();
@@ -260,8 +260,8 @@ public:
             const Glib::ustring& tip,
             const Glib::ustring& key,
             Registry& wr,
-            Inkscape::XML::Node* repr_in = NULL,
-            SPDocument *doc_in = NULL );
+            Inkscape::XML::Node* repr_in = nullptr,
+            SPDocument *doc_in = nullptr );
 
 protected:
     sigc::connection  _activate_connection;
@@ -278,8 +278,8 @@ public:
                            const Glib::ustring& ckey,
                            const Glib::ustring& akey,
                            Registry& wr,
-                           Inkscape::XML::Node* repr_in = NULL,
-                           SPDocument *doc_in = NULL);
+                           Inkscape::XML::Node* repr_in = nullptr,
+                           SPDocument *doc_in = nullptr);
 
     void setRgba32 (guint32);
     void closeWindow();
@@ -298,8 +298,8 @@ public:
                                 const Glib::ustring& suffix,
                                 const Glib::ustring& key,
                                 Registry& wr,
-                                Inkscape::XML::Node* repr_in = NULL,
-                                SPDocument *doc_in = NULL );
+                                Inkscape::XML::Node* repr_in = nullptr,
+                                SPDocument *doc_in = nullptr );
 
     bool setProgrammatically; // true if the value was set by setValue, not changed by the user;
                                 // if a callback checks it, it must reset it back to false
@@ -319,8 +319,8 @@ public:
                                 const Glib::ustring& tip2,
                                 const Glib::ustring& key,
                                 Registry& wr,
-                                Inkscape::XML::Node* repr_in = NULL,
-                                SPDocument *doc_in = NULL );
+                                Inkscape::XML::Node* repr_in = nullptr,
+                                SPDocument *doc_in = nullptr );
 
     void setValue (bool second);
 
@@ -339,8 +339,8 @@ public:
                       const Glib::ustring& tip,
                       const Glib::ustring& key,
                       Registry& wr,
-                      Inkscape::XML::Node* repr_in = NULL,
-                      SPDocument *doc_in = NULL );
+                      Inkscape::XML::Node* repr_in = nullptr,
+                      SPDocument *doc_in = nullptr );
 
 protected:
     sigc::connection  _value_x_changed_connection;
@@ -356,8 +356,8 @@ public:
                                   const Glib::ustring& tip,
                                   const Glib::ustring& key,
                                   Registry& wr,
-                                  Inkscape::XML::Node* repr_in = NULL,
-                                  SPDocument *doc_in = NULL );
+                                  Inkscape::XML::Node* repr_in = nullptr,
+                                  SPDocument *doc_in = nullptr );
 
     // redefine setValue, because transform must be applied
     void setValue(Geom::Point const & p);
@@ -380,8 +380,8 @@ public:
                       const Glib::ustring& tip,
                       const Glib::ustring& key,
                       Registry& wr,
-                      Inkscape::XML::Node* repr_in = NULL,
-                      SPDocument *doc_in = NULL );
+                      Inkscape::XML::Node* repr_in = nullptr,
+                      SPDocument *doc_in = nullptr );
 
     // redefine setValue, because transform must be applied
     void setValue(Geom::Point const & p);
@@ -411,8 +411,8 @@ public:
                        const Glib::ustring& tip,
                        const Glib::ustring& key,
                        Registry& wr,
-                       Inkscape::XML::Node* repr_in = NULL,
-                       SPDocument *doc_in = NULL);
+                       Inkscape::XML::Node* repr_in = nullptr,
+                       SPDocument *doc_in = nullptr);
 
     void setValue (double val, long startseed);
 
@@ -429,8 +429,8 @@ public:
                              const Glib::ustring& tip,
                              const Glib::ustring& key,
                              Registry& wr,
-                             Inkscape::XML::Node* repr_in = NULL,
-                             SPDocument *doc_in = NULL);
+                             Inkscape::XML::Node* repr_in = nullptr,
+                             SPDocument *doc_in = nullptr);
 
     void setValue (Glib::ustring fontspec);
 
diff --git a/src/ui/widget/scalar-unit.cpp b/src/ui/widget/scalar-unit.cpp
index 4fa1a7584..fc8c92142 100644
--- a/src/ui/widget/scalar-unit.cpp
+++ b/src/ui/widget/scalar-unit.cpp
@@ -34,7 +34,7 @@ ScalarUnit::ScalarUnit(Glib::ustring const &label, Glib::ustring const &tooltip,
       _absolute_is_increment(false),
       _percentage_is_increment(false)
 {
-    if (_unit_menu == NULL) {
+    if (_unit_menu == nullptr) {
         _unit_menu = new UnitMenu();
         g_assert(_unit_menu);
         _unit_menu->setUnitType(unit_type);
@@ -70,7 +70,7 @@ ScalarUnit::ScalarUnit(Glib::ustring const &label, Glib::ustring const &tooltip,
 
 void ScalarUnit::initScalar(double min_value, double max_value)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     Scalar::setDigits(_unit_menu->getDefaultDigits());
     Scalar::setIncrements(_unit_menu->getDefaultStep(),
                           _unit_menu->getDefaultPage());
@@ -79,7 +79,7 @@ void ScalarUnit::initScalar(double min_value, double max_value)
 
 bool ScalarUnit::setUnit(Glib::ustring const &unit)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     // First set the unit
     if (!_unit_menu->setUnit(unit)) {
         return false;
@@ -90,21 +90,21 @@ bool ScalarUnit::setUnit(Glib::ustring const &unit)
 
 void ScalarUnit::setUnitType(UnitType unit_type)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     _unit_menu->setUnitType(unit_type);
     lastUnits = _unit_menu->getUnitAbbr();
 }
 
 void ScalarUnit::resetUnitType(UnitType unit_type)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     _unit_menu->resetUnitType(unit_type);
     lastUnits = _unit_menu->getUnitAbbr();
 }
 
 Unit const * ScalarUnit::getUnit() const
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     return _unit_menu->getUnit();
 }
 
@@ -116,14 +116,14 @@ UnitType ScalarUnit::getUnitType() const
 
 void ScalarUnit::setValue(double number, Glib::ustring const &units)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     _unit_menu->setUnit(units);
     Scalar::setValue(number);
 }
 
 void ScalarUnit::setValueKeepUnit(double number, Glib::ustring const &units)
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     if (units == "") {
         // set the value in the default units
         Scalar::setValue(number);
@@ -140,7 +140,7 @@ void ScalarUnit::setValue(double number)
 
 double ScalarUnit::getValue(Glib::ustring const &unit_name) const
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
     if (unit_name == "") {
         // Return the value in the default units
         return Scalar::getValue();
@@ -223,7 +223,7 @@ void  ScalarUnit::setFromPercentage(double value)
 
 void ScalarUnit::on_unit_changed()
 {
-    g_assert(_unit_menu != NULL);
+    g_assert(_unit_menu != nullptr);
 
     Glib::ustring abbr = _unit_menu->getUnitAbbr();
     _suffix->set_label(abbr);
diff --git a/src/ui/widget/scalar-unit.h b/src/ui/widget/scalar-unit.h
index 9e310d3bd..debcff53e 100644
--- a/src/ui/widget/scalar-unit.h
+++ b/src/ui/widget/scalar-unit.h
@@ -52,7 +52,7 @@ public:
                UnitType unit_type = UNIT_TYPE_LINEAR,
                Glib::ustring const &suffix = "",
                Glib::ustring const &icon = "",
-               UnitMenu *unit_menu = NULL,
+               UnitMenu *unit_menu = nullptr,
                bool mnemonic = true);
 
     /**
diff --git a/src/ui/widget/scalar.cpp b/src/ui/widget/scalar.cpp
index 937bea697..a3fff0c8c 100644
--- a/src/ui/widget/scalar.cpp
+++ b/src/ui/widget/scalar.cpp
@@ -54,13 +54,13 @@ Scalar::Scalar(Glib::ustring const &label, Glib::ustring const &tooltip,
 
 unsigned Scalar::getDigits() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<SpinButton*>(_widget)->get_digits();
 }
 
 double Scalar::getStep() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     double step, page;
     static_cast<SpinButton*>(_widget)->get_increments(step, page);
     return step;
@@ -68,7 +68,7 @@ double Scalar::getStep() const
 
 double Scalar::getPage() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     double step, page;
     static_cast<SpinButton*>(_widget)->get_increments(step, page);
     return page;
@@ -76,7 +76,7 @@ double Scalar::getPage() const
 
 double Scalar::getRangeMin() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     double min, max;
     static_cast<SpinButton*>(_widget)->get_range(min, max);
     return min;
@@ -84,7 +84,7 @@ double Scalar::getRangeMin() const
 
 double Scalar::getRangeMax() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     double min, max;
     static_cast<SpinButton*>(_widget)->get_range(min, max);
     return max;
@@ -92,38 +92,38 @@ double Scalar::getRangeMax() const
 
 double Scalar::getValue() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<SpinButton*>(_widget)->get_value();
 }
 
 int Scalar::getValueAsInt() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<SpinButton*>(_widget)->get_value_as_int();
 }
 
 
 void Scalar::setDigits(unsigned digits)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     static_cast<SpinButton*>(_widget)->set_digits(digits);
 }
 
 void Scalar::setIncrements(double step, double /*page*/)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     static_cast<SpinButton*>(_widget)->set_increments(step, 0);
 }
 
 void Scalar::setRange(double min, double max)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     static_cast<SpinButton*>(_widget)->set_range(min, max);
 }
 
 void Scalar::setValue(double value, bool setProg)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     if (setProg) {
         setProgrammatically = true; // callback is supposed to reset back, if it cares
     }
@@ -132,7 +132,7 @@ void Scalar::setValue(double value, bool setProg)
 
 void Scalar::update()
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     static_cast<SpinButton*>(_widget)->update();
 }
 
diff --git a/src/ui/widget/selected-style.cpp b/src/ui/widget/selected-style.cpp
index a15afde4c..c0b0a7f56 100644
--- a/src/ui/widget/selected-style.cpp
+++ b/src/ui/widget/selected-style.cpp
@@ -74,7 +74,7 @@ ss_selection_modified( Inkscape::Selection *selection, guint /*flags*/, gpointer
 static void
 ss_subselection_changed( gpointer /*dragger*/, gpointer data )
 {
-    ss_selection_changed (NULL, data);
+    ss_selection_changed (nullptr, data);
 }
 
 namespace {
@@ -121,9 +121,9 @@ SelectedStyle::SelectedStyle(bool /*layout*/)
     :
       current_stroke_width(0),
 
-      _sw_unit(NULL),
+      _sw_unit(nullptr),
 
-      _desktop (NULL),
+      _desktop (nullptr),
       _table(),
       _fill_label (_("Fill:")),
       _stroke_label (_("Stroke:")),
@@ -146,7 +146,7 @@ SelectedStyle::SelectedStyle(bool /*layout*/)
       _opacity_blocked (false)
 {
     set_name("SelectedStyle");
-    _drop[0] = _drop[1] = 0;
+    _drop[0] = _drop[1] = nullptr;
     _dropEnabled[0] = _dropEnabled[1] = false;
 
     _fill_label.set_halign(Gtk::ALIGN_START);
@@ -207,7 +207,7 @@ SelectedStyle::SelectedStyle(bool /*layout*/)
         _lgradient[i].show_all();
         __lgradient[i] = (i == SS_FILL)? (_("Linear gradient fill")) : (_("Linear gradient stroke"));
 
-        _gradient_preview_l[i] =  GTK_WIDGET(sp_gradient_image_new (NULL));
+        _gradient_preview_l[i] =  GTK_WIDGET(sp_gradient_image_new (nullptr));
         _gradient_box_l[i].pack_start(_lgradient[i]);
         _gradient_box_l[i].pack_start(*(Glib::wrap(_gradient_preview_l[i])));
         _gradient_box_l[i].show_all();
@@ -217,7 +217,7 @@ SelectedStyle::SelectedStyle(bool /*layout*/)
         _rgradient[i].show_all();
         __rgradient[i] = (i == SS_FILL)? (_("Radial gradient fill")) : (_("Radial gradient stroke"));
 
-        _gradient_preview_r[i] = GTK_WIDGET(sp_gradient_image_new (NULL));
+        _gradient_preview_r[i] = GTK_WIDGET(sp_gradient_image_new (nullptr));
         _gradient_box_r[i].pack_start(_rgradient[i]);
         _gradient_box_r[i].pack_start(*(Glib::wrap(_gradient_preview_r[i])));
         _gradient_box_r[i].show_all();
@@ -228,7 +228,7 @@ SelectedStyle::SelectedStyle(bool /*layout*/)
         _mgradient[i].show_all();
         __mgradient[i] = (i == SS_FILL)? (_("Mesh gradient fill")) : (_("Mesh gradient stroke"));
 
-        _gradient_preview_m[i] = GTK_WIDGET(sp_gradient_image_new (NULL));
+        _gradient_preview_m[i] = GTK_WIDGET(sp_gradient_image_new (nullptr));
         _gradient_box_m[i].pack_start(_mgradient[i]);
         _gradient_box_m[i].pack_start(*(Glib::wrap(_gradient_preview_m[i])));
         _gradient_box_m[i].show_all();
@@ -925,7 +925,7 @@ void SelectedStyle::on_popup_preset(int i) {
 void
 SelectedStyle::update()
 {
-    if (_desktop == NULL)
+    if (_desktop == nullptr)
         return;
 
     // create temporary style
@@ -1201,7 +1201,7 @@ RotateableSwatch::RotateableSwatch(SelectedStyle *parent, guint mode) :
     startcolor(0),
     startcolor_set(false),
     undokey("ssrot1"),
-    cr(0),
+    cr(nullptr),
     cr_set(false)
 
 {
@@ -1285,7 +1285,7 @@ RotateableSwatch::do_motion(double by, guint modifier) {
 
     if (!scrolling && !cr_set) {
         GtkWidget *w = GTK_WIDGET(gobj());
-        GdkPixbuf *pixbuf = NULL;
+        GdkPixbuf *pixbuf = nullptr;
 
         if (modifier == 2) { // saturation
             pixbuf = gdk_pixbuf_new_from_xpm_data((const gchar **)cursor_adj_s_xpm);
@@ -1297,13 +1297,13 @@ RotateableSwatch::do_motion(double by, guint modifier) {
             pixbuf = gdk_pixbuf_new_from_xpm_data((const gchar **)cursor_adj_h_xpm);
         }
 
-	if (pixbuf != NULL) {
+	if (pixbuf != nullptr) {
 	    cr = gdk_cursor_new_from_pixbuf(gdk_display_get_default(), pixbuf, 16, 16);
 
             g_object_unref(pixbuf);	    
             gdk_window_set_cursor(gtk_widget_get_window(w), cr);
 	    g_object_unref(cr);
-	    cr = NULL;
+	    cr = nullptr;
             cr_set = true;
         }
     }
@@ -1364,10 +1364,10 @@ RotateableSwatch::do_release(double by, guint modifier) {
 
     if (cr_set) {
         GtkWidget *w = GTK_WIDGET(gobj());
-        gdk_window_set_cursor(gtk_widget_get_window(w), NULL);
+        gdk_window_set_cursor(gtk_widget_get_window(w), nullptr);
         if (cr) {
            g_object_unref(cr);
-           cr = NULL;
+           cr = nullptr;
         }
         cr_set = false;
     }
@@ -1495,7 +1495,7 @@ Dialog::FillAndStroke *get_fill_and_stroke_panel(SPDesktop *desktop)
         } catch (std::exception &e) { }
     }
 
-    return 0;
+    return nullptr;
 }
 
 } // namespace Widget
diff --git a/src/ui/widget/spin-scale.cpp b/src/ui/widget/spin-scale.cpp
index 94b178a43..0c843590c 100644
--- a/src/ui/widget/spin-scale.cpp
+++ b/src/ui/widget/spin-scale.cpp
@@ -161,7 +161,7 @@ void DualSpinScale::set_from_attribute(SPObject* o)
             if(toks[1])
                 v2 = Glib::Ascii::strtod(toks[1]);
 
-            _link.set_active(toks[1] == 0);
+            _link.set_active(toks[1] == nullptr);
 
             _s1.get_adjustment()->set_value(v1);
             _s2.get_adjustment()->set_value(v2);
diff --git a/src/ui/widget/spin-slider.cpp b/src/ui/widget/spin-slider.cpp
index 03981763d..0b63e7455 100644
--- a/src/ui/widget/spin-slider.cpp
+++ b/src/ui/widget/spin-slider.cpp
@@ -153,7 +153,7 @@ void DualSpinSlider::set_from_attribute(SPObject* o)
             if(toks[1])
                 v2 = Glib::Ascii::strtod(toks[1]);
 
-            _link.set_active(toks[1] == 0);
+            _link.set_active(toks[1] == nullptr);
 
             _s1.get_adjustment()->set_value(v1);
             _s2.get_adjustment()->set_value(v2);
diff --git a/src/ui/widget/spin-slider.h b/src/ui/widget/spin-slider.h
index cd2d2a427..fe03c85d3 100644
--- a/src/ui/widget/spin-slider.h
+++ b/src/ui/widget/spin-slider.h
@@ -32,7 +32,7 @@ class SpinSlider : public Gtk::HBox, public AttrWidget
 {
 public:
     SpinSlider(double value, double lower, double upper, double step_inc,
-	       double climb_rate, int digits, const SPAttributeEnum a = SP_ATTR_INVALID, const char* tip_text = NULL);
+	       double climb_rate, int digits, const SPAttributeEnum a = SP_ATTR_INVALID, const char* tip_text = nullptr);
 
     Glib::ustring get_as_attribute() const override;
     void set_from_attribute(SPObject*) override;
diff --git a/src/ui/widget/spinbutton.cpp b/src/ui/widget/spinbutton.cpp
index 0c082d3ce..777a6edf4 100644
--- a/src/ui/widget/spinbutton.cpp
+++ b/src/ui/widget/spinbutton.cpp
@@ -35,7 +35,7 @@ int SpinButton::on_input(double* newvalue)
     try {
         Inkscape::Util::EvaluatorQuantity result;
         if (_unit_menu || _unit_tracker) {
-            Unit const *unit = NULL;
+            Unit const *unit = nullptr;
             if (_unit_menu) {
                 unit = _unit_menu->getUnit();
             } else {
@@ -48,7 +48,7 @@ int SpinButton::on_input(double* newvalue)
                 throw Inkscape::Util::EvaluatorException("Input dimensions do not match with parameter dimensions.","");
             }
         } else {
-            Inkscape::Util::ExpressionEvaluator eval = Inkscape::Util::ExpressionEvaluator(get_text().c_str(), NULL);
+            Inkscape::Util::ExpressionEvaluator eval = Inkscape::Util::ExpressionEvaluator(get_text().c_str(), nullptr);
             result = eval.evaluate();
         }
 
diff --git a/src/ui/widget/spinbutton.h b/src/ui/widget/spinbutton.h
index a252743be..28d9849a8 100644
--- a/src/ui/widget/spinbutton.h
+++ b/src/ui/widget/spinbutton.h
@@ -30,16 +30,16 @@ class SpinButton : public Gtk::SpinButton
 public:
   SpinButton(double climb_rate = 0.0, guint digits = 0)
     : Gtk::SpinButton(climb_rate, digits),
-      _unit_menu(NULL),
-      _unit_tracker(NULL),
+      _unit_menu(nullptr),
+      _unit_tracker(nullptr),
       _on_focus_in_value(0.)
   {
       connect_signals();
   };
   explicit SpinButton(Glib::RefPtr<Gtk::Adjustment>& adjustment, double climb_rate = 0.0, guint digits = 0)
     : Gtk::SpinButton(adjustment, climb_rate, digits),
-      _unit_menu(NULL),
-      _unit_tracker(NULL),
+      _unit_menu(nullptr),
+      _unit_tracker(nullptr),
       _on_focus_in_value(0.)
   {
       connect_signals();
diff --git a/src/ui/widget/style-subject.cpp b/src/ui/widget/style-subject.cpp
index e23627080..5eccc67cf 100644
--- a/src/ui/widget/style-subject.cpp
+++ b/src/ui/widget/style-subject.cpp
@@ -17,11 +17,11 @@ namespace Inkscape {
 namespace UI {
 namespace Widget {
 
-StyleSubject::StyleSubject() : _desktop(NULL) {
+StyleSubject::StyleSubject() : _desktop(nullptr) {
 }
 
 StyleSubject::~StyleSubject() {
-    setDesktop(NULL);
+    setDesktop(nullptr);
 }
 
 void StyleSubject::setDesktop(SPDesktop *desktop) {
@@ -49,7 +49,7 @@ Inkscape::Selection *StyleSubject::Selection::_getSelection() const {
     if (desktop) {
         return desktop->getSelection();
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
@@ -102,7 +102,7 @@ void StyleSubject::Selection::setCSS(SPCSSAttr *css) {
 }
 
 StyleSubject::CurrentLayer::CurrentLayer() {
-    _element = NULL;
+    _element = nullptr;
 }
 
 StyleSubject::CurrentLayer::~CurrentLayer() {
@@ -112,12 +112,12 @@ void StyleSubject::CurrentLayer::_setLayer(SPObject *layer) {
     _layer_release.disconnect();
     _layer_modified.disconnect();
     if (_element) {
-        sp_object_unref(_element, NULL);
+        sp_object_unref(_element, nullptr);
     }
     _element = layer;
     if (layer) {
-        sp_object_ref(layer, NULL);
-        _layer_release = layer->connectRelease(sigc::hide(sigc::bind(sigc::mem_fun(*this, &CurrentLayer::_setLayer), (SPObject *)NULL)));
+        sp_object_ref(layer, nullptr);
+        _layer_release = layer->connectRelease(sigc::hide(sigc::bind(sigc::mem_fun(*this, &CurrentLayer::_setLayer), (SPObject *)nullptr)));
         _layer_modified = layer->connectModified(sigc::hide(sigc::hide(sigc::mem_fun(*this, &CurrentLayer::_emitChanged))));
     }
     _emitChanged();
@@ -171,7 +171,7 @@ void StyleSubject::CurrentLayer::_afterDesktopSwitch(SPDesktop *desktop) {
         _layer_switched = desktop->connectCurrentLayerChanged(sigc::mem_fun(*this, &CurrentLayer::_setLayer));
         _setLayer(desktop->currentLayer());
     } else {
-        _setLayer(NULL);
+        _setLayer(nullptr);
     }
 }
 
diff --git a/src/ui/widget/style-swatch.cpp b/src/ui/widget/style-swatch.cpp
index 15928e300..04a63271e 100644
--- a/src/ui/widget/style-swatch.cpp
+++ b/src/ui/widget/style-swatch.cpp
@@ -106,13 +106,13 @@ void StyleSwatch::ToolObserver::notify(Inkscape::Preferences::Entry const &val)
 
 StyleSwatch::StyleSwatch(SPCSSAttr *css, gchar const *main_tip)
     :
-      _desktop(NULL),
+      _desktop(nullptr),
       _verb_t(0),
-      _css(NULL),
-      _tool_obs(NULL),
-      _style_obs(NULL),
+      _css(nullptr),
+      _tool_obs(nullptr),
+      _style_obs(nullptr),
       _table(Gtk::manage(new Gtk::Grid())),
-      _sw_unit(NULL)
+      _sw_unit(nullptr)
 {
     set_name("StyleSwatch");
     
@@ -201,7 +201,7 @@ StyleSwatch::on_click(GdkEventButton */*event*/)
     if (this->_desktop && this->_verb_t != SP_VERB_NONE) {
         Inkscape::Verb *verb = Inkscape::Verb::get(this->_verb_t);
         SPAction *action = verb->get_action(Inkscape::ActionContext((Inkscape::UI::View::View *) this->_desktop));
-        sp_action_perform (action, NULL);
+        sp_action_perform (action, nullptr);
         return true;
     }
     return false;
@@ -227,7 +227,7 @@ StyleSwatch::setWatchedTool(const char *path, bool synthesize)
     
     if (_tool_obs) {
         delete _tool_obs;
-        _tool_obs = NULL;
+        _tool_obs = nullptr;
     }
 
     if (path) {
diff --git a/src/ui/widget/text.cpp b/src/ui/widget/text.cpp
index e6795b138..5b6b7468d 100644
--- a/src/ui/widget/text.cpp
+++ b/src/ui/widget/text.cpp
@@ -30,13 +30,13 @@ Text::Text(Glib::ustring const &label, Glib::ustring const &tooltip,
 
 Glib::ustring const Text::getText() const
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     return static_cast<Gtk::Entry*>(_widget)->get_text();
 }
 
 void Text::setText(Glib::ustring const text)
 {
-    g_assert(_widget != NULL);
+    g_assert(_widget != nullptr);
     setProgrammatically = true; // callback is supposed to reset back, if it cares
     static_cast<Gtk::Entry*>(_widget)->set_text(text); // FIXME: set correctly
 }
diff --git a/src/ui/widget/tolerance-slider.cpp b/src/ui/widget/tolerance-slider.cpp
index d2c338571..447efdfe0 100644
--- a/src/ui/widget/tolerance-slider.cpp
+++ b/src/ui/widget/tolerance-slider.cpp
@@ -46,7 +46,7 @@ namespace Widget {
 //====================================================
 
 ToleranceSlider::ToleranceSlider(const Glib::ustring& label1, const Glib::ustring& label2, const Glib::ustring& label3, const Glib::ustring& tip1, const Glib::ustring& tip2, const Glib::ustring& tip3, const Glib::ustring& key, Registry& wr)
-: _vbox(0)
+: _vbox(nullptr)
 {
     init(label1, label2, label3, tip1, tip2, tip3, key, wr);
 }
diff --git a/src/ui/widget/unit-tracker.cpp b/src/ui/widget/unit-tracker.cpp
index e7e47af4b..bb9425b29 100644
--- a/src/ui/widget/unit-tracker.cpp
+++ b/src/ui/widget/unit-tracker.cpp
@@ -33,7 +33,7 @@ namespace Widget {
 UnitTracker::UnitTracker(UnitType unit_type) :
     _active(0),
     _isUpdating(false),
-    _activeUnit(NULL),
+    _activeUnit(nullptr),
     _activeUnitInitialized(false),
     _store(nullptr),
     _priorValues()