code: public <NR> @NonNull Pair<L, NR> rmap(final @NonNull Function<? super R, ? extends NR> function) {
      return new Pair<>(this.left, function.apply(this.right));
    }
docs: Map the right value of this pair.
  
  @param function the function
  @param <NR> the right type
  @return a new pair