description

# removeFirst method Null safety

E removeFirst ()
override

Removes and returns the first element of this queue.

The queue must not be empty when this method is called.

## Implementation

    E removeFirst() {
      _DoubleLinkedQueueEntry<E> firstEntry =
          _sentinel._nextLink as _DoubleLinkedQueueEntry<E>;
      E result = firstEntry._remove();
      _elementCount--;
      return result;
    }