Remove Linked List Elements (LeetCode)

Problem: Remove Linked List Elements
Remove all elements from a linked list of integers that have value val.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        //if(head==NULL) return NULL;
        ListNode* dummy = new ListNode(0);
        dummy->next = head;
        
        while(head!=NULL && head->val == val) 
        {
            head = head->next;
            dummy->next = head;
        }
        
        if(head==NULL) return NULL;
        
        while(head->next!=NULL)
        {
            if(head->next->val == val)
                head->next = head->next->next;
            else head=head->next;
        }
        return dummy->next;
    }
};