Added required check

git-svn-id: https://svn.inf.ethz.ch/svn/lecturers/a2/trunk@7172 8c9fc860-2736-0410-a75d-ab315db34111

source/Generic.Modules.Mod

@@ -678,7 +678,7 @@ BEGIN
 		(* clean up finalizers *)
 		m := root;
 		WHILE m # NIL DO
-			IF LEN(m.code)>0 THEN
+			IF (m.code # NIL) & (LEN(m.code)>0) THEN
 				Heaps.CleanupModuleFinalizers(ADDRESSOF(m.code[0]), LEN(m.code), m.name)
 			END;
 			m := m.next