code: <B> MutatorResult<B> map(final Function<? super T, ? extends B> mapper) {
  		requireNonNull(mapper);
  		return of(mapper.apply(_result), _mutations);
  	}
docs: Maps this mutation result to type {@code B} using the given {@code mapper}.
  
  @param mapper the mutation result mapper
  @param <B> the new mutation result type
  @return a new mapped mutation result
  @throws NullPointerException if the given {@code mapper} is {@code null}