Leetcoder - Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path 1->2->3 which represents the number 123.
Find the total sum of all root-to-leaf numbers.
For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Return the sum = 12 + 13 = 25.


/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(root==null) {
            return 0;
        }
        return getSum(root, 0, 0);
    }
   
    public int getSum(TreeNode node, int currentVal, int sum) {
        currentVal = currentVal * 10 + node.val;
        if(node.left==null && node.right==null) {
            sum += currentVal;
        }
        if(node.left!=null) {
            sum = getSum(node.left, currentVal, sum);
        }
        if(node.right!=null) {
            sum = getSum(node.right, currentVal, sum);
        }
        return sum;
    }
}