Java : This function is to search through a binary tree left and right and return a count of the nodes above depth k. This is what I have so far, but I'm getting a Null pointer exception.

public class MyIntSET {

private Node root;

private static class Node {

public final int key;

public Node left, right;

public Node(int key) { this.key = key; }

}

public int sizeAboveDepth(int k) {

return abovehelp(root, k, 0);

}

public int abovehelp(Node x, int k, int count) {

int szl = abovehelp(x.left, k, count);

int szr = abovehelp(x.right, k, count);

if (x != null && count > k) {

count ++;

return 1 + szl + szr;

}

count ++;

return 0 + szl + szr;

}