boot_defclass: super may be NULL

src/class.c

@@ -731,8 +731,13 @@ boot_defclass(mrb_state *mrb, struct RClass *super)
   struct RClass *c;
 
   c = (struct RClass*)mrb_obj_alloc(mrb, MRB_TT_CLASS, mrb->class_class);
-  c->super = super ? super : mrb->object_class;
+  if (super) {
+    c->super = super;
     mrb_field_write_barrier(mrb, (struct RBasic*)c, (struct RBasic*)super);
+  }
+  else {
+    c->super = mrb->object_class;
+  }
   c->mt = kh_init(mt, mrb);
   return c;
 }