code: @NotNull
      public <R> Stream<R> mapToObj(@NotNull final LongFunction<? extends R> mapper) {
          return new Stream<R>(params, new LongMapToObj<R>(iterator, mapper));
      }
docs: Returns a {@code Stream} consisting of the results of applying the given
  function to the elements of this stream.
  
  <p> This is an intermediate operation.
  
  @param <R> the type result
  @param mapper  the mapper function used to apply to each element
  @return the new {@code Stream}