code: public static <T> List<T> singletonList(T element) {
  		if (element == null) {
  			return Collections.emptyList();
  		}
  		return Collections.singletonList(element);
  	}
docs: Replies a singleton list with the given element, or the empty list if
  the element is <code>null</code>.
  
  @param <T> the type of the element in the list.
  @param element the element.
  @return the list with the element, or the empty list.