I keep getting this error. Could you help me with it? Thanks!

public static final class LinkedQueue implements QueueInterface { private Node firstNode; private Node lastNode;

public LinkedQueue() { firstNode = null; lastNode = null; }

@Override public T getFront() { if (isEmpty()) { return null; } return firstNode.getData(); }

@Override public boolean isEmpty() { return firstNode == null; }

@Override public void clear() { firstNode = null; lastNode = null;

}

public class Node { private E data; // Entry in bag private Node next; // Link to next node

public Node(E dataPortion) { this(dataPortion, null); } // end constructor

public Node(E dataPortion, Node nextNode) { data = dataPortion; next = nextNode; } // end constructor

public E getData() { if (data != null) { return data; } return null; }

public Node getNext() { return next; }

public void setNext(Node newNext) { next = newNext; }

} // end LinkedQueue

2.0 / 3.0 Result Behavior 1/** 2 @precondition: queue is not empty 3 @return value from removed node that was at the front of the queue 4 5@Override 6 public T dequeue() { 7 if (isEmpty()) return null; 9 I frontValue = getFront(); 10 firstNode.setData(null); 11 firstNode = firstNode.getNext(); 12 Dequeue updates first node Dequeue updates properly when empty Expected: but was: Dequeue updates properly when not empty 13 14 return frontValue; 15 16]} 17