• 在主方法内向removeElements方法内传入head参数为null时就会触发，导致无法进行下面的判断，调试时在方法内部进行判断head是否为空前就触发了异常，不知道如何解决

class Solution {
public ListNode removeElements(ListNode head, int val) {

    if (head == null){
        return null;
    }

    while(head.val == val && head != null){
        ListNode delNode = head;
        head = head.next;
        delNode.next = null;
    }

    ListNode prev = head;
    while (prev.next != null){
        if(prev.next.val == val){
            ListNode delNode = prev.next;
            prev.next = delNode.next;
            delNode.next = null;
        }
        else{
            prev = prev.next;
        }
    }
    return head;
}

public static void main(String[] args) {
    ListNode head = null;
    Solution s = new Solution();
    String s1 = s.removeElements(head,1).toString();
    System.out.println(s1);
}

}