Queue impl using linked list

Queue impl

public class Queue<T> {
    private static class Node<T> {
        private T data;
        private Node<T> next;
        
        public Node(T data) {
            this.data = data;
        }
    }
    
    public Node<T> firstNode;
    public Node<T> lastNode;
    
    public void add(T item) {
        Node<T> newNode = new Node<>(item);
        
        if (lastNode != null) {
            lastNode.next = newNode;
        }
        
        lastNode = newNode;
        
        if (firstNode == null) {
            firstNode = lastNode;
        }
    }
    
    public T remove() {
        if (firstNode == null) {
            return null;
        }
        
        T data = firstNode.data;
        firstNode = firstNode.next;
        
        if (firstNode == null) {
            lastNode == null;
        }
        
        return data;
    }
    
    public T peek() {
        if (firstNode == null) {
            return null;
        }
        
        return firstNode.data;
    }
    
    public boolean isEmpty() {
        return firstNode == null;
    }
}