Use mrb_true_or_false_value() / in mrb_hash_has_keyWithKey().

src/hash.c

@@ -1013,14 +1013,17 @@ mrb_hash_has_keyWithKey(mrb_state *mrb, mrb_value hash, mrb_value key)
 {
   khash_t(ht) *h = RHASH_TBL(hash);
   khiter_t k;
+  mrb_bool result;
 
   if (h) {
     k = kh_get(ht, h, key);
-    if (k != kh_end(h))
-      return mrb_true_value();
+    result = (k != kh_end(h));
+  }
+  else {
+    result = 0;
   }
 
-  return mrb_false_value();
+  return mrb_true_or_false_value(result);
 }
 
 /* 15.2.13.4.13 */