问如何在Java中插入双向链表中的第一个元素

EN

public void add(ListNode prev, Object object, ListNode next){
    ListNode newNode = new ListNode(prev, object, next);
    prev.setNext(newNode);  
    newNode.setPrevious(prev);
    newNode.setNext(next);
    next.setPrevious(newNode);
}

int currNum = scanner.nextInt();
DoublyLL dll = new DoublyLL();
ListNode curr = dll.getFirst(); //start at beginning of list
ListNode prev = null;

if(curr == null){   //if the list is empty
    ListNode first = new ListNode(curr, currNum, null);
    dll.getFirst().setValue(first); //returns a null-pointer exception
}