code: public Datatype.Builder mapBuilderFactory(UnaryOperator<BuilderFactory> mapper) {
      return setBuilderFactory(getBuilderFactory().map(mapper));
    }
docs: If the value to be returned by {@link Datatype#getBuilderFactory()} is present, replaces it by
  applying {@code mapper} to it and using the result.
  
  <p>If the result is null, clears the value.
  
  @return this {@code Builder} object
  @throws NullPointerException if {@code mapper} is null