Index: trunk/src/obj_common.c
===================================================================
--- trunk/src/obj_common.c	(revision 11947)
+++ trunk/src/obj_common.c	(revision 11948)
@@ -178,14 +178,15 @@
 const char *pcb_obj_id_invalid(const char *id)
 {
 	const char *s;
-	for(s = id; *s != '\0'; s++) {
-		if (isalnum(*s))
-			continue;
-		switch(*s) {
-			case '_': case '.': case '$': case ':': continue;
+	if (id != NULL)
+		for(s = id; *s != '\0'; s++) {
+			if (isalnum(*s))
+				continue;
+			switch(*s) {
+				case '_': case '.': case '$': case ':': continue;
+			}
+			return s;
 		}
-		return s;
-	}
 	return NULL;
 }