From 2e5b32b3554e821b422ae63b72dd1a2200065ae1 Mon Sep 17 00:00:00 2001
From: Dirk Lemstra <dirk@git.imagemagick.org>
Date: Sun, 8 Jul 2018 16:32:00 +0200
Subject: [PATCH] GetImageMask returns NULL when the image does not have the
 specified mask.

---
 MagickCore/image.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/MagickCore/image.c b/MagickCore/image.c
index fa262378d..d4d5000ce 100644
--- a/MagickCore/image.c
+++ b/MagickCore/image.c
@@ -1453,6 +1453,24 @@ MagickExport Image *GetImageMask(const Image *image,const PixelMask type,
   if (image->debug != MagickFalse)
     (void) LogMagickEvent(TraceEvent,GetMagickModule(),"...");
   assert(image->signature == MagickCoreSignature);
+  switch (type)
+  {
+    case ReadPixelMask:
+    {
+      if ((image->channels & ReadMaskChannel) == 0)
+        return((Image *) NULL);
+    }
+    case WritePixelMask:
+    {
+      if ((image->channels & WriteMaskChannel) == 0)
+        return((Image *) NULL);
+    }
+    default:
+    {
+      if ((image->channels & CompositeMaskChannel) == 0)
+        return((Image *) NULL);
+    }
+  }
   mask_image=AcquireImage((ImageInfo *) NULL,exception);
   status=SetImageExtent(mask_image,image->columns,image->rows,exception);
   if (status == MagickFalse)
-- 
2.40.0