@Override
  public E element() {
    return getFirst();
  }
Retrieves, but does not remove, the head of the queue represented by
this deque.  This method differs from {@link #peek peek} only in that
it throws an exception if this deque is empty.
<br>
This method is equivalent to {@link #getFirst() getFirst}.

@return the head of the queue represented by this deque
@throws NoSuchElementException if this deque is empty
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/PriorityBlockingDeque.java