Remove Duplicates from Sorted List

Remove Duplicates from Sorted List 

Given a sorted linked list, delete all duplicates such that each element appear only once.

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

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode first;
            ListNode second;
            if(null == head)
                return null;
            first = head;
            second = head.next;
            while(second != null){
                while(null != second && first.val == second.val){
                    first.next = second.next;
                    second = first.next;
                }
                first = first.next;
                if(null != second)
                    second = second.next;
            }
            return head;
    }
}