code: @NotNull
      @SuppressWarnings("unchecked")
      public static <T> Stream<T> ofNullable(@Nullable T element) {
          return (element == null) ? Stream.<T>empty() : Stream.of(element);
      }
docs: If specified element is null, returns an empty {@code Stream},
  otherwise returns a {@code Stream} containing a single element.
  
  @param <T> the type of the stream element
  @param element  the element to be passed to stream if it is non-null
  @return the new stream
  @since 1.1.5