default <V>Generator<V> andThen(Function<? super T,? extends V> after){
  Objects.requireNonNull(after);
  return null;
}

default < V > Generator < V > andThen ( Function < ? super T , ? extends V > after ) { Objects . requireNonNull ( after ) ; return null ; }
produce a generator of type v by applying the supplied function to this generator ' s values
