private E innerRemoveLast() {
    E l = list.pollLast();
    if (l == null)
      return null;

    notFull.signal();
    return l;
  }
Removes and returns last element, or null if empty.

@return The removed element.
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/PriorityBlockingDeque.java