Queue using a linked list

Queue.java

class Queue<T> {

    private static class Node<D> {
        private D data;
        private Node<D> previous;
        private Node<D> next;

        private Node(D data) {
            this.data = data;
        }
    }

    private int size;
    private Node<T> head;
    private Node<T> tail;

    T getFirst() {
        return head == null ? null : head.data;
    }

    T getLast() {
        return tail == null ? null : tail.data;
    }

    void add(T data) {
        Node<T> n = new Node<>(data);
        size++;
        if (head == null || tail == null) {
            head = tail = n;
            return;
        }

        n.next = tail;
        tail.previous = n;
        tail = n;
    }

    T remove() {
        if (head == null) {
            return null;
        }

        Node<T> n = head;
        head = head.previous;
        size--;

        return n.data;
    }

    T peek() {
        return head == null ? null : head.data;
    }

    int length() {
        return size;
    }

}