Index: generic/nsf.c
===================================================================
diff -u -r1a7f8ba5a64328222a30016f19769f6595a74ace -r6adb5d9759c3159a2da1e4f7cedebfcfb9a29123
--- generic/nsf.c	(.../nsf.c)	(revision 1a7f8ba5a64328222a30016f19769f6595a74ace)
+++ generic/nsf.c	(.../nsf.c)	(revision 6adb5d9759c3159a2da1e4f7cedebfcfb9a29123)
@@ -18839,7 +18839,9 @@
     /*
      * Remove dependent filters of this class from all subclasses
      */
-    FilterRemoveDependentFilterCmds(cl, subClasses);
+    if (subClasses != NULL) {
+      FilterRemoveDependentFilterCmds(cl, subClasses);
+    }
 
 #if defined(NSF_WITH_ASSERTIONS)
     if (clopt->assertions != NULL) {