commit 8abe475b7dde75961ea46b9cb69aa7d658d002f3
Author: Eric S. Raymond <esr@thyrsus.com>
Date:   Wed Jun 10 17:00:29 2026 -0400

    Resolve ticket #203: GifUnionColorMap NULL Pointer Dereference

diff --git gifalloc.c gifalloc.c
index 886907d..e36684b 100644
--- gifalloc.c
+++ gifalloc.c
@@ -114,6 +114,10 @@ ColorMapObject *GifUnionColorMap(const ColorMapObject *ColorIn1,
 	int i, j, CrntSlot, RoundUpTo, NewGifBitSize;
 	ColorMapObject *ColorUnion;
 
+	if (ColorIn1 == NULL || ColorIn2 == NULL) {
+		return (NULL);
+	}
+
 	/*
 	 * We don't worry about duplicates within either color map; if
 	 * the caller wants to resolve those, he can perform unions