outer might be NULL; close #428

src/variable.c

@@ -905,13 +905,16 @@ mrb_class_sym(mrb_state *mrb, struct RClass *c, struct RClass *outer)
 
   name = mrb_obj_iv_get(mrb, (struct RObject*)c, mrb_intern(mrb, "__classid__"));
   if (mrb_nil_p(name)) {
+
+    if (!outer) return 0;
+    else {
       struct csym_arg arg;
 
       arg.c = c;
       arg.sym = 0;
-
       iv_foreach(mrb, outer->iv, csym_i, &arg);
       return arg.sym;
     }
+  }
   return SYM2ID(name);
 }