code: public static LongStreamEx of(OptionalLong optional) {
          return optional.isPresent() ? of(optional.getAsLong()) : empty();
      }
docs: Returns a sequential {@code LongStreamEx} containing an
  {@link OptionalLong} value, if present, otherwise returns an empty
  {@code LongStreamEx}.
  
  @param optional the optional to create a stream of
  @return a stream with an {@code OptionalLong} value if present, otherwise
  an empty stream
  @since 0.1.1