FIFO queue structure based on a singly linked list

In the java course I'm following right now, I'm required to implement a FIFO queue structure based on a singly linked list. I have to implement interface and override 3 methods: add, poll and peek.

I'm stuck with poll and peek and can not get an Object in return statement. Or may be there is another way to do it. For any help would be very grateful.

add -Use add() method to add elements into the Queue
poll - Fetching and removing the element at the head of the queue
peek- as pool without removing

public class Queue<T> implements Queue2<T> {

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

    @Override
    public boolean add(T e) {

        Node<T> node = new Node(e);

        if (head == null) {
            head = node;
            tail = node;
        } else {

            tail.next = node;
            tail = node;
            node.next = null;
        }
        size++;
        return true;
    }


    @Override
    public T poll() {
        if (size == 0)
            return null;
        else {
            T obj = head.getObject();
            head = head.next;
            if (head == null) {
                tail = null;
            }
            size--;

            return obj;
        }

    }

    @Override

    public T peek() {
        if (head == null)
            return null;
        else {

            return head.getObject();

        }
    }


    class Node<T> {
        Node<T> next;

        Node<T> value;

        public <T> Node(T value) {


        }

        public T getObject() {
            **return null;** // what should be returned here?
        }
    }
}

 public static void main(String[] args) {
        Queue<String> queue1 = new Queue<>();
        queue1.add("finns");
        queue1.add("bella");
        queue1.add("ssara");
        queue1.add("nanna");
        queue1.add("anna");
       System.out.println(queue1.peek());
       System.out.println(queue1.poll());