public BuildableType.Builder mapMergeBuilder(UnaryOperator<MergeBuilderMethod> mapper) {
    Objects.requireNonNull(mapper);
    return mergeBuilder(mapper.apply(mergeBuilder()));
  }
public BuildableType . Builder mapMergeBuilder ( UnaryOperator < MergeBuilderMethod > mapper ) { Objects . requireNonNull ( mapper ) ; return mergeBuilder ( mapper . apply ( mergeBuilder ( ) ) ) ; }
Replaces the value to be returned by {@link BuildableType#mergeBuilder()} by applying {@code
mapper} to it and using the result.

@return this {@code Builder} object
@throws NullPointerException if {@code mapper} is null or returns null
@throws IllegalStateException if the field has not been set