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

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

11 files changed, 86 insertions, 86 deletions

diff --git a/src/trace/filterset.cpp b/src/trace/filterset.cpp
index f6c025956..db6d16eea 100644
--- a/src/trace/filterset.cpp
+++ b/src/trace/filterset.cpp
@@ -48,7 +48,7 @@ GrayMap *grayMapGaussian(GrayMap *me)
 
     GrayMap *newGm = GrayMapCreate(width, height);
     if (!newGm)
-        return NULL;
+        return nullptr;
 
     for (int y = 0 ; y<height ; y++)
         {
@@ -98,7 +98,7 @@ RgbMap *rgbMapGaussian(RgbMap *me)
 
     RgbMap *newGm = RgbMapCreate(width, height);
     if (!newGm)
-        return NULL;
+        return nullptr;
 
     for (int y = 0 ; y<height ; y++)
         {
@@ -178,7 +178,7 @@ static GrayMap *grayMapSobel(GrayMap *gm,
 
     GrayMap *newGm = GrayMapCreate(width, height);
     if (!newGm)
-        return NULL;
+        return nullptr;
 
     for (int y = 0 ; y<height ; y++)
         {
@@ -353,11 +353,11 @@ GrayMap *
 grayMapCanny(GrayMap *gm, double lowThreshold, double highThreshold)
 {
     if (!gm)
-        return NULL;
+        return nullptr;
 
     GrayMap *cannyGm = grayMapSobel(gm, lowThreshold, highThreshold);
     if (!cannyGm)
-        return NULL;
+        return nullptr;
     /*cannyGm->writePPM(cannyGm, "canny.ppm");*/
 
     return cannyGm;
diff --git a/src/trace/imagemap-gdk.cpp b/src/trace/imagemap-gdk.cpp
index 298414074..db8bbdd99 100644
--- a/src/trace/imagemap-gdk.cpp
+++ b/src/trace/imagemap-gdk.cpp
@@ -10,7 +10,7 @@
 GrayMap *gdkPixbufToGrayMap(GdkPixbuf *buf)
 {
     if (!buf)
-        return NULL;
+        return nullptr;
 
     int width       = gdk_pixbuf_get_width(buf);
     int height      = gdk_pixbuf_get_height(buf);
@@ -20,7 +20,7 @@ GrayMap *gdkPixbufToGrayMap(GdkPixbuf *buf)
 
     GrayMap *grayMap = GrayMapCreate(width, height);
     if (!grayMap)
-        return NULL;
+        return nullptr;
 
     //### Fill in the odd cells with RGB values
     int x,y;
@@ -46,19 +46,19 @@ GrayMap *gdkPixbufToGrayMap(GdkPixbuf *buf)
 GdkPixbuf *grayMapToGdkPixbuf(GrayMap *grayMap)
 {
     if (!grayMap)
-        return NULL;
+        return nullptr;
 
     guchar *pixdata = (guchar *)
           malloc(sizeof(guchar) * grayMap->width * grayMap->height * 3);
     if (!pixdata)
-        return NULL;
+        return nullptr;
 
     int n_channels = 3;
     int rowstride  = grayMap->width * 3;
 
     GdkPixbuf *buf = gdk_pixbuf_new_from_data(pixdata, GDK_COLORSPACE_RGB,
                         0, 8, grayMap->width, grayMap->height,
-                        rowstride, (GdkPixbufDestroyNotify)g_free, NULL);
+                        rowstride, (GdkPixbufDestroyNotify)g_free, nullptr);
 
     //### Fill in the odd cells with RGB values
     int x,y;
@@ -87,7 +87,7 @@ GdkPixbuf *grayMapToGdkPixbuf(GrayMap *grayMap)
 PackedPixelMap *gdkPixbufToPackedPixelMap(GdkPixbuf *buf)
 {
     if (!buf)
-        return NULL;
+        return nullptr;
 
     int width       = gdk_pixbuf_get_width(buf);
     int height      = gdk_pixbuf_get_height(buf);
@@ -97,7 +97,7 @@ PackedPixelMap *gdkPixbufToPackedPixelMap(GdkPixbuf *buf)
 
     PackedPixelMap *ppMap = PackedPixelMapCreate(width, height);
     if (!ppMap)
-        return NULL;
+        return nullptr;
 
     //### Fill in the cells with RGB values
     int x,y;
@@ -130,7 +130,7 @@ PackedPixelMap *gdkPixbufToPackedPixelMap(GdkPixbuf *buf)
 RgbMap *gdkPixbufToRgbMap(GdkPixbuf *buf)
 {
     if (!buf)
-        return NULL;
+        return nullptr;
 
     int width       = gdk_pixbuf_get_width(buf);
     int height      = gdk_pixbuf_get_height(buf);
@@ -140,7 +140,7 @@ RgbMap *gdkPixbufToRgbMap(GdkPixbuf *buf)
 
     RgbMap *rgbMap = RgbMapCreate(width, height);
     if (!rgbMap)
-        return NULL;
+        return nullptr;
 
     //### Fill in the cells with RGB values
     int x,y;
@@ -175,19 +175,19 @@ RgbMap *gdkPixbufToRgbMap(GdkPixbuf *buf)
 GdkPixbuf *indexedMapToGdkPixbuf(IndexedMap *iMap)
 {
     if (!iMap)
-        return NULL;
+        return nullptr;
 
     guchar *pixdata = (guchar *)
           malloc(sizeof(guchar) * iMap->width * iMap->height * 3);
     if (!pixdata)
-        return NULL;
+        return nullptr;
 
     int n_channels = 3;
     int rowstride  = iMap->width * 3;
 
     GdkPixbuf *buf = gdk_pixbuf_new_from_data(pixdata, GDK_COLORSPACE_RGB,
                         0, 8, iMap->width, iMap->height,
-                        rowstride, (GdkPixbufDestroyNotify)g_free, NULL);
+                        rowstride, (GdkPixbufDestroyNotify)g_free, nullptr);
 
     //### Fill in the cells with RGB values
     int x,y;
diff --git a/src/trace/imagemap.cpp b/src/trace/imagemap.cpp
index a8d8a8c8f..e2e97d5ec 100644
--- a/src/trace/imagemap.cpp
+++ b/src/trace/imagemap.cpp
@@ -65,7 +65,7 @@ GrayMap *GrayMapCreate(int width, int height)
 
     GrayMap *me = (GrayMap *)malloc(sizeof(GrayMap));
     if (!me)
-        return NULL;
+        return nullptr;
 
     /** methods **/
     me->setPixel    = gSetPixel;
@@ -81,7 +81,7 @@ GrayMap *GrayMapCreate(int width, int height)
     if (!me->pixels)
         {
         free(me);
-        return NULL;
+        return nullptr;
         }
     me->rows = (unsigned long **)
               malloc(sizeof(unsigned long *) *  height);
@@ -89,7 +89,7 @@ GrayMap *GrayMapCreate(int width, int height)
         {
         free(me->pixels);
         free(me);
-        return NULL;
+        return nullptr;
         }
 
     unsigned long *row = me->pixels;
@@ -179,7 +179,7 @@ PackedPixelMap *PackedPixelMapCreate(int width, int height)
 
     PackedPixelMap *me = (PackedPixelMap *)malloc(sizeof(PackedPixelMap));
     if (!me)
-        return NULL;
+        return nullptr;
 
     /** methods **/
     me->setPixel     = ppSetPixel;
@@ -195,13 +195,13 @@ PackedPixelMap *PackedPixelMapCreate(int width, int height)
     me->pixels = (unsigned long *) malloc(sizeof(unsigned long) * width * height);
     if (!me->pixels){
         free(me);
-        return NULL;
+        return nullptr;
     }
     me->rows = (unsigned long **) malloc(sizeof(unsigned long *) * height);
     if (!me->rows){
         free(me->pixels); //allocated as me->pixels is not NULL here: see previous check
         free(me);
-        return NULL;
+        return nullptr;
     }
     
     unsigned long *row = me->pixels;
@@ -288,7 +288,7 @@ RgbMap *RgbMapCreate(int width, int height)
 
     RgbMap *me = (RgbMap *)malloc(sizeof(RgbMap));
     if (!me){
-        return NULL;
+        return nullptr;
     }
     
     /** methods **/
@@ -305,13 +305,13 @@ RgbMap *RgbMapCreate(int width, int height)
     me->pixels = (RGB *) malloc(sizeof(RGB) * width * height);
     if (!me->pixels){
         free(me);
-        return NULL;
+        return nullptr;
     }
     me->rows = (RGB **) malloc(sizeof(RGB *) * height);
     if (!me->rows){
         free(me->pixels); //allocated as me->pixels is not NULL here: see previous check
         free(me);
-        return NULL;
+        return nullptr;
     }
 
     RGB *row = me->pixels;
@@ -398,7 +398,7 @@ IndexedMap *IndexedMapCreate(int width, int height)
 
     IndexedMap *me = (IndexedMap *)malloc(sizeof(IndexedMap));
     if (!me)
-        return NULL;
+        return nullptr;
 
     /** methods **/
     me->setPixel      = iSetPixel;
@@ -414,13 +414,13 @@ IndexedMap *IndexedMapCreate(int width, int height)
     me->pixels = (unsigned int *) malloc(sizeof(unsigned int) * width * height);
     if (!me->pixels){
         free(me);
-        return NULL;
+        return nullptr;
     }
     me->rows = (unsigned int **) malloc(sizeof(unsigned int *) * height);
     if (!me->rows){
         free(me->pixels); //allocated as me->pixels is not NULL here: see previous check
         free(me);
-        return NULL;
+        return nullptr;
     }
 
     unsigned int *row = me->pixels;
diff --git a/src/trace/pool.h b/src/trace/pool.h
index 88fd82bcd..b4693d941 100644
--- a/src/trace/pool.h
+++ b/src/trace/pool.h
@@ -62,9 +62,9 @@ class pool {
   {
       cblock = 0;
       size = sizeof(T) > sizeof(void *) ? sizeof(T) : sizeof(void *);
-      next = NULL;
+      next = nullptr;
       for (int k = 0; k < 64; k++) {
-          block[k] = NULL;
+          block[k] = nullptr;
       }
   }
 
diff --git a/src/trace/potrace/bitmap.h b/src/trace/potrace/bitmap.h
index 7b5a94bb1..a47de24d0 100644
--- a/src/trace/potrace/bitmap.h
+++ b/src/trace/potrace/bitmap.h
@@ -63,12 +63,12 @@ static inline potrace_bitmap_t *bm_new(int w, int h) {
   /* check for overflow error */
   if (size < 0 || (h != 0 && dy != 0 && size / h / dy != BM_WORDSIZE)) {
     errno = ENOMEM;
-    return NULL;
+    return nullptr;
   }
 
   bm = (potrace_bitmap_t *) malloc(sizeof(potrace_bitmap_t));
   if (!bm) {
-    return NULL;
+    return nullptr;
   }
   bm->w = w;
   bm->h = h;
@@ -76,7 +76,7 @@ static inline potrace_bitmap_t *bm_new(int w, int h) {
   bm->map = (potrace_word *) malloc(size);
   if (!bm->map) {
     free(bm);
-    return NULL;
+    return nullptr;
   }
   return bm;
 }
@@ -94,7 +94,7 @@ static inline potrace_bitmap_t *bm_dup(const potrace_bitmap_t *bm) {
   potrace_bitmap_t *bm1 = bm_new(bm->w, bm->h);
   ptrdiff_t size = (ptrdiff_t)bm->dy * (ptrdiff_t)bm->h * (ptrdiff_t)BM_WORDSIZE;
   if (!bm1) {
-    return NULL;
+    return nullptr;
   }
   memcpy(bm1->map, bm->map, size);
   return bm1;
diff --git a/src/trace/potrace/inkscape-potrace.cpp b/src/trace/potrace/inkscape-potrace.cpp
index b438be248..86658653a 100644
--- a/src/trace/potrace/inkscape-potrace.cpp
+++ b/src/trace/potrace/inkscape-potrace.cpp
@@ -207,9 +207,9 @@ static long writePaths(PotraceTracingEngine *engine, potrace_path_t *plist,
 static GrayMap *filter(PotraceTracingEngine &engine, GdkPixbuf * pixbuf)
 {
     if (!pixbuf)
-        return NULL;
+        return nullptr;
 
-    GrayMap *newGm = NULL;
+    GrayMap *newGm = nullptr;
 
     /*### Color quantization -- banding ###*/
     if (engine.getTraceType() == TRACE_QUANT)
@@ -281,9 +281,9 @@ static GrayMap *filter(PotraceTracingEngine &engine, GdkPixbuf * pixbuf)
 static IndexedMap *filterIndexed(PotraceTracingEngine &engine, GdkPixbuf * pixbuf)
 {
     if (!pixbuf)
-        return NULL;
+        return nullptr;
 
-    IndexedMap *newGm = NULL;
+    IndexedMap *newGm = nullptr;
 
     RgbMap *gm = gdkPixbufToRgbMap(pixbuf);
     if (engine.getMultiScanSmooth())
@@ -326,7 +326,7 @@ PotraceTracingEngine::preview(Glib::RefPtr<Gdk::Pixbuf> thePixbuf)
         {
         IndexedMap *gm = filterIndexed(*this, pixbuf);
         if (!gm)
-            return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+            return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 
         Glib::RefPtr<Gdk::Pixbuf> newBuf =
              Glib::wrap(indexedMapToGdkPixbuf(gm), false);
@@ -339,7 +339,7 @@ PotraceTracingEngine::preview(Glib::RefPtr<Gdk::Pixbuf> thePixbuf)
         {
         GrayMap *gm = filter(*this, pixbuf);
         if (!gm)
-            return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+            return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 
         Glib::RefPtr<Gdk::Pixbuf> newBuf =
             Glib::wrap(grayMapToGdkPixbuf(gm), false);
diff --git a/src/trace/quantize.cpp b/src/trace/quantize.cpp
index c386c0ee9..a7868fd03 100644
--- a/src/trace/quantize.cpp
+++ b/src/trace/quantize.cpp
@@ -165,10 +165,10 @@ inline int childIndex(RGB rgb)
 inline Ocnode *ocnodeNew(pool<Ocnode> *pool)
 {
     Ocnode *node = pool->draw();
-    node->ref = NULL;
-    node->parent = NULL;
+    node->ref = nullptr;
+    node->parent = nullptr;
     node->nchild = 0;
-    for (int i = 0; i < 8; i++) node->child[i] = NULL;
+    for (int i = 0; i < 8; i++) node->child[i] = nullptr;
     node->mi = 0;
     return node;
 }
@@ -363,7 +363,7 @@ static void ocnodeStrip(pool<Ocnode> *pool, Ocnode **ref, int *count, unsigned l
         if (!node->mi) ocnodeMi(node); //mi generation may be required
 	if (node->mi > lvl) return; //leaf is above strip level
         ocnodeFree(pool, node);
-        *ref = NULL;
+        *ref = nullptr;
         (*count)--;
         }
     else
@@ -373,7 +373,7 @@ static void ocnodeStrip(pool<Ocnode> *pool, Ocnode **ref, int *count, unsigned l
         node->nchild = 0;
         node->nleaf = 0;
         node->mi = 0;
-        Ocnode **lonelychild = NULL;
+        Ocnode **lonelychild = nullptr;
         for (int i = 0; i < 8; i++) if (node->child[i])
             {
             ocnodeStrip(pool, &node->child[i], count, lvl);
@@ -402,7 +402,7 @@ static void ocnodeStrip(pool<Ocnode> *pool, Ocnode **ref, int *count, unsigned l
                 node->nleaf = 1;
 		ocnodeMi(node);
                 ocnodeFree(pool, *lonelychild);
-                *lonelychild = NULL;
+                *lonelychild = nullptr;
                 }
             else
                 {
@@ -444,21 +444,21 @@ static void octreeBuildArea(pool<Ocnode> *pool, RgbMap *rgbmap, Ocnode **ref,
 {
     int dx = x2 - x1, dy = y2 - y1;
     int xm = x1 + dx/2, ym = y1 + dy/2;
-    Ocnode *ref1 = NULL;
-    Ocnode *ref2 = NULL;
+    Ocnode *ref1 = nullptr;
+    Ocnode *ref2 = nullptr;
     if (dx == 1 && dy == 1)
         ocnodeLeaf(pool, ref, rgbmap->getPixel(rgbmap, x1, y1));
     else if (dx > dy)
         {
 	octreeBuildArea(pool, rgbmap, &ref1, x1, y1, xm, y2, ncolor);
 	octreeBuildArea(pool, rgbmap, &ref2, xm, y1, x2, y2, ncolor);
-	octreeMerge(pool, NULL, ref, ref1, ref2);
+	octreeMerge(pool, nullptr, ref, ref1, ref2);
 	}
     else
         {
 	octreeBuildArea(pool, rgbmap, &ref1, x1, y1, x2, ym, ncolor);
 	octreeBuildArea(pool, rgbmap, &ref2, x1, ym, x2, y2, ncolor);
-	octreeMerge(pool, NULL, ref, ref1, ref2);
+	octreeMerge(pool, nullptr, ref, ref1, ref2);
 	}
 
     //octreePrune(ref, 2*ncolor);
@@ -472,7 +472,7 @@ static void octreeBuildArea(pool<Ocnode> *pool, RgbMap *rgbmap, Ocnode **ref,
 static Ocnode *octreeBuild(pool<Ocnode> *pool, RgbMap *rgbmap, int ncolor)
 {
     //create the octree
-    Ocnode *node = NULL;
+    Ocnode *node = nullptr;
     octreeBuildArea(pool,
                     rgbmap, &node,
                     0, 0, rgbmap->width, rgbmap->height, ncolor
@@ -549,11 +549,11 @@ IndexedMap *rgbMapQuantize(RgbMap *rgbmap, int ncolor)
     assert(rgbmap);
     assert(ncolor > 0);
 
-    IndexedMap *newmap = 0;
+    IndexedMap *newmap = nullptr;
 
     pool<Ocnode> pool;
 
-    Ocnode *tree = 0;
+    Ocnode *tree = nullptr;
     try {
         tree = octreeBuild(&pool, rgbmap, ncolor);
     }
diff --git a/src/trace/siox.cpp b/src/trace/siox.cpp
index 9df4e561c..9501da3c4 100644
--- a/src/trace/siox.cpp
+++ b/src/trace/siox.cpp
@@ -344,8 +344,8 @@ SioxImage::SioxImage(unsigned int widthArg, unsigned int heightArg)
  */
 SioxImage::SioxImage(const SioxImage &other)
 {
-    pixdata = NULL;
-    cmdata  = NULL;
+    pixdata = nullptr;
+    cmdata  = nullptr;
     assign(other);
 }
 
@@ -654,14 +654,14 @@ GdkPixbuf *SioxImage::getGdkPixbuf()
     guchar *pixdata = (guchar *)
           malloc(sizeof(guchar) * width * height * n_channels);
     if (!pixdata)
-        return NULL;
+        return nullptr;
 
     int rowstride  = width * n_channels;
 
     GdkPixbuf *buf = gdk_pixbuf_new_from_data(pixdata,
                         GDK_COLORSPACE_RGB,
                         has_alpha, 8, width, height,
-                        rowstride, NULL, NULL);
+                        rowstride, nullptr, nullptr);
 
     //### Fill in the cells with RGB values
     int row  = 0;
@@ -728,14 +728,14 @@ const float Siox::CERTAIN_BACKGROUND_CONFIDENCE=0.0f;
  *  Construct a Siox engine
  */
 Siox::Siox() :
-    sioxObserver(0),
+    sioxObserver(nullptr),
     keepGoing(true),
     width(0),
     height(0),
     pixelCount(0),
-    image(0),
-    cm(0),
-    labelField(0)
+    image(nullptr),
+    cm(nullptr),
+    labelField(nullptr)
 {
     init();
 }
@@ -749,9 +749,9 @@ Siox::Siox(SioxObserver *observer) :
     width(0),
     height(0),
     pixelCount(0),
-    image(0),
-    cm(0),
-    labelField(0)
+    image(nullptr),
+    cm(nullptr),
+    labelField(nullptr)
 {
     init();
 }
diff --git a/src/trace/siox.h b/src/trace/siox.h
index fa18ac238..6f3f89a83 100644
--- a/src/trace/siox.h
+++ b/src/trace/siox.h
@@ -388,7 +388,7 @@ public:
      *  used to point to a C++ object or C state object, to delegate
      *  callback processing to something else.  Use NULL to ignore.
      */
-    SioxObserver(void *contextArg) : context(NULL)
+    SioxObserver(void *contextArg) : context(nullptr)
         { context = contextArg; }
 
     /**
diff --git a/src/trace/trace.cpp b/src/trace/trace.cpp
index bd52d7a57..a76be208e 100644
--- a/src/trace/trace.cpp
+++ b/src/trace/trace.cpp
@@ -49,7 +49,7 @@ SPImage *Tracer::getSelectedSPImage()
     if (!desktop)
         {
         g_warning("Trace: No active desktop");
-        return NULL;
+        return nullptr;
         }
 
     Inkscape::MessageStack *msgStack = desktop->getMessageStack();
@@ -60,12 +60,12 @@ SPImage *Tracer::getSelectedSPImage()
         char *msg = _("Select an <b>image</b> to trace");
         msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
         //g_warning(msg);
-        return NULL;
+        return nullptr;
         }
 
     if (sioxEnabled)
         {
-        SPImage *img = NULL;
+        SPImage *img = nullptr;
         auto list = sel->items();
         std::vector<SPItem *> items;
         sioxShapes.clear();
@@ -94,7 +94,7 @@ SPImage *Tracer::getSelectedSPImage()
                     {
                     char *msg = _("Select only one <b>image</b> to trace");
                     msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
-                    return NULL;
+                    return nullptr;
                     }
                 img = SP_IMAGE(item);
                 }
@@ -112,7 +112,7 @@ SPImage *Tracer::getSelectedSPImage()
             {
             char *msg = _("Select one image and one or more shapes above it");
             msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
-            return NULL;
+            return nullptr;
             }
         return img;
         }
@@ -125,7 +125,7 @@ SPImage *Tracer::getSelectedSPImage()
             char *msg = _("Select an <b>image</b> to trace");  //same as above
             msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
             //g_warning(msg);
-            return NULL;
+            return nullptr;
             }
 
         if (!SP_IS_IMAGE(item))
@@ -133,7 +133,7 @@ SPImage *Tracer::getSelectedSPImage()
             char *msg = _("Select an <b>image</b> to trace");
             msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
             //g_warning(msg);
-            return NULL;
+            return nullptr;
             }
 
         SPImage *img = SP_IMAGE(item);
@@ -215,7 +215,7 @@ Glib::RefPtr<Gdk::Pixbuf> Tracer::sioxProcessImage(SPImage *img, Glib::RefPtr<Gd
     if (!desktop)
         {
         g_warning("%s", _("Trace: No active desktop"));
-        return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+        return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
         }
 
     Inkscape::MessageStack *msgStack = desktop->getMessageStack();
@@ -226,7 +226,7 @@ Glib::RefPtr<Gdk::Pixbuf> Tracer::sioxProcessImage(SPImage *img, Glib::RefPtr<Gd
         char *msg = _("Select an <b>image</b> to trace");
         msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
         //g_warning(msg);
-        return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+        return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
         }
 
     Inkscape::DrawingItem *aImg = img->get_arenaitem(desktop->dkey);
@@ -313,7 +313,7 @@ Glib::RefPtr<Gdk::Pixbuf> Tracer::sioxProcessImage(SPImage *img, Glib::RefPtr<Gd
     if (!result.isValid())
         {
         g_warning("%s", _("Invalid SIOX result"));
-        return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+        return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
         }
 
     //result.writePPM("siox2.ppm");
@@ -334,10 +334,10 @@ Glib::RefPtr<Gdk::Pixbuf> Tracer::getSelectedImage()
 
     SPImage *img = getSelectedSPImage();
     if (!img)
-        return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+        return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 
     if (!img->pixbuf)
-        return Glib::RefPtr<Gdk::Pixbuf>(NULL);
+        return Glib::RefPtr<Gdk::Pixbuf>(nullptr);
 
     GdkPixbuf *raw_pb = img->pixbuf->getPixbufRaw(false);
     GdkPixbuf *trace_pb = gdk_pixbuf_copy(raw_pb);
@@ -408,7 +408,7 @@ void Tracer::traceThread()
         char *msg = _("Trace: No active document");
         msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
         //g_warning(msg);
-        engine = NULL;
+        engine = nullptr;
         return;
         }
     SPDocument *doc = SP_ACTIVE_DOCUMENT;
@@ -418,7 +418,7 @@ void Tracer::traceThread()
     SPImage *img = getSelectedSPImage();
     if (!img)
         {
-        engine = NULL;
+        engine = nullptr;
         return;
         }
 
@@ -440,7 +440,7 @@ void Tracer::traceThread()
         char *msg = _("Trace: Image has no bitmap data");
         msgStack->flash(Inkscape::ERROR_MESSAGE, msg);
         //g_warning(msg);
-        engine = NULL;
+        engine = nullptr;
         return;
         }
 
@@ -455,7 +455,7 @@ void Tracer::traceThread()
     //### Check if we should stop
     if (!keepGoing || nrPaths<1)
         {
-        engine = NULL;
+        engine = nullptr;
         return;
         }
 
@@ -498,7 +498,7 @@ void Tracer::traceThread()
     //#OK.  Now let's start making new nodes
 
     Inkscape::XML::Document *xml_doc = desktop->doc()->getReprDoc();
-    Inkscape::XML::Node *groupRepr = NULL;
+    Inkscape::XML::Node *groupRepr = nullptr;
 
     //# if more than 1, make a <g>roup of <path>s
     if (nrPaths > 1)
@@ -519,7 +519,7 @@ void Tracer::traceThread()
         pathRepr->setAttribute("d",     result.getPathData().c_str());
 
         if (nrPaths > 1)
-            groupRepr->addChild(pathRepr, NULL);
+            groupRepr->addChild(pathRepr, nullptr);
         else
             par->addChild(pathRepr, imgRepr);
 
@@ -549,7 +549,7 @@ void Tracer::traceThread()
     //## inform the document, so we can undo
     DocumentUndo::done(doc, SP_VERB_SELECTION_TRACE, _("Trace bitmap"));
 
-    engine = NULL;
+    engine = nullptr;
 
     char *msg = g_strdup_printf(_("Trace: Done. %ld nodes created"), totalNodeCount);
     msgStack->flash(Inkscape::NORMAL_MESSAGE, msg);
diff --git a/src/trace/trace.h b/src/trace/trace.h
index b6b7684d0..790298261 100644
--- a/src/trace/trace.h
+++ b/src/trace/trace.h
@@ -167,7 +167,7 @@ public:
      */
     Tracer()
         {
-        engine       = NULL;
+        engine       = nullptr;
         sioxEnabled  = false;
         }