code: public E peekFirst() {
          final Node<E> f = first;
          return (f == null) ? null : f.item;
       }
docs: Retrieves, but does not remove, the first element of this list,
  or returns {@code null} if this list is empty.
  
  @return the first element of this list, or {@code null}
  if this list is empty
  @since 1.6