diff -urNp old/converter/other/svgtopam.c new/converter/other/svgtopam.c
--- old/converter/other/svgtopam.c	2017-02-08 12:11:02.593690917 +0100
+++ new/converter/other/svgtopam.c	2017-02-08 12:13:05.192846469 +0100
@@ -676,7 +676,7 @@ stringToUint(const char *   const string
 
     /* TODO: move this to nstring.c */
 
-    if (strlen(string) == 0)
+    if (string == NULL || strlen(string) == 0)
         pm_asprintf(errorP, "Value is a null string");
     else {
         char * tailptr;