Populating Next Right Pointers in Each Node II LeetCode

/**
 * Definition for binary tree with next pointer.
 * public class TreeLinkNode {
 *     int val;
 *     TreeLinkNode left, right, next;
 *     TreeLinkNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void connect(TreeLinkNode root) {
        if (root == null){
            return ;
        }
        Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int qSize = queue.size();
            TreeLinkNode preNode = null;
            for (int i = 0; i < qSize; i++){
                TreeLinkNode curNode = queue.poll();
                curNode.next = preNode;
                preNode = curNode;
                if (curNode.right != null){
                    queue.offer(curNode.right);
                }
                if (curNode.left != null){
                    queue.offer(curNode.left);
                }
            }
        }
    }
}