code: public boolean offer(E e) {
          if (e == null) throw new NullPointerException();
          return transferer.transfer(e, true, 0) != null;
      }
docs: Inserts the specified element into this queue, if another thread is
  waiting to receive it.
  
  @param e the element to add
  @return {@code true} if the element was added to this queue, else
  {@code false}
  @throws NullPointerException if the specified element is null