Implementing Priority Queue by Linked List in Java

Question

I'm working on Priority Queue in Java implementing by Linked List, to set the priority order, I'm trying to shift all the Linked List Objects to array for sorting, and then again back to the Linked List (after sorting priority wise). I tried this code but I get "Null pointer exception" every time I pass Linked List Object to Array. What should I do?

public class Node {

    Node next;
    Object data;
    int pref;

    Node() {
        this(0, null);
    }

    Node(Object m, Node s) {
        setData(m);
        next = s;
    }

    Node(Object m, Node s, int pref) {
        setData(m);
        next = s;
        this.pref = pref;
    }

    void setData(Object m) {

        data = m;
    }

    public Object getData() {
        return data;
    }

    public void setPref(int pref){
        this.pref = pref;
    }

    public int getPref(){
        return pref;
    }
}




 public class PriorityQueue(){
    public Node head;
    PriorityQueue(){
    head = null;
    }
    public boolean enQueue(Object v, int p) {

            Node newNode = new Node();
            newNode.setData(v);
            newNode.setPref(p);

            if (head == null) {

                newNode.next = head;
                head = newNode;
                return true;

            } else {

                Node current = head;

                try {

                    while (current.next != null) {
                        current = current.next;
                    }
                    current.next = newNode;
                    settingPriorityLevel();
                    return true;

                } catch (java.lang.OutOfMemoryError e) {
                    System.out.println(e.getMessage());
                    return false;
                }
            }

        }

        public void settingPriorityLevel(){

            Node arr[] = null;      //converting LinkedList to array for sorting purpose
            Node current = head;
            Node temp;

            for(int i = 0; i <= size(); i++){
                arr[i] = current;

                current = current.next;
            }

            for(int i=0; i < arr.length; i++){              //sorting
                for(int j = i+1; j < arr.length; j++){
                    if(arr[i].pref > arr[j].pref){
                    temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                    }
                }
            }

            for(int i = 0; i < arr.length; i++){        //shifting back to LinkedList
                current = arr[i];
                current = current.next;
            }


        }
    }