code: public BuildableType.Builder mergeBuilder(MergeBuilderMethod mergeBuilder) {
      this.mergeBuilder = Objects.requireNonNull(mergeBuilder);
      _unsetProperties.remove(Property.MERGE_BUILDER);
      return (BuildableType.Builder) this;
    }
docs: Sets the value to be returned by {@link BuildableType#mergeBuilder()}.
  
  @return this {@code Builder} object
  @throws NullPointerException if {@code mergeBuilder} is null