code: @NotNull
      public <R> Stream<R> map(@NotNull final Function<? super T, ? extends R> mapper) {
          return new Stream<R>(params, new ObjMap<T, R>(iterator, mapper));
      }
docs: Returns {@code Stream} with elements that obtained by applying the given function.
  
  <p>This is an intermediate operation.
  
  <p>Example:
  <pre>
  mapper: (a) -&gt; a + 5
  stream: [1, 2, 3, 4]
  result: [6, 7, 8, 9]
  </pre>
  
  @param <R> the type of elements in resulting stream
  @param mapper  the mapper function used to apply to each element
  @return the new stream