code: @NotNull
      public LongStream map(@NotNull final LongUnaryOperator mapper) {
          return new LongStream(params, new LongMap(iterator, mapper));
      }
docs: Returns an {@code LongStream} consisting of the results of applying the given
  function to the elements of this stream.
  
  <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 mapper  the mapper function used to apply to each element
  @return the new stream
  @see Stream#map(com.annimon.stream.function.Function)