code: public JSType build() {
       // If we have an empty record, simply return the object type.
      if (isEmpty) {
         return registry.getNativeObjectType(JSTypeNative.OBJECT_TYPE);
      }
      ImmutableSortedMap.Builder<String, RecordProperty> m = ImmutableSortedMap.naturalOrder();
      m.putAll(this.properties);
      return new RecordType(registry, m.build(), isDeclared);
    }
docs: Creates a record. Fails if any duplicate property names were added.
  @return The record type.