Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,

Given 1->2->3->3->4->4->5, return 1->2->5.

Given 1->1->1->2->3, return 2->3.

public ListNode deleteDuplicates(ListNode head) {
        if (head==null||head.next==null) {
            return head;
        }
        //safeguard
        ListNode newHead = new ListNode(0);
        ListNode current = head;
        ListNode previous = newHead;
        newHead.next = current;

        while(current!=null&&current.next!=null) {
            ListNode next = current.next;
            if (next.val == current.val) {
                //next until current and next value are different
                while (next!=null && next.val==current.val) {
                    next = next.next;
                }
                //set previous point to next
                previous.next = next;
            //if value is not the same, set previous point to current
            } else {
                previous = current;
            }
            //current should point to next
            current = next;
        }

        return newHead.next;
    }