Remove all leaf nodes from a Generic Tree or N-ary Tree

// Java Code to delete all leaf nodes in
// an N-ary tree
import java.util.ArrayList;
import java.util.Iterator;

class Node {
    int data;
    ArrayList<Node> children;

    Node(int val) {
        data = val;
        children = new ArrayList<>();
    }
}

class GfG {

    // Recursive function to delete all leaf nodes
    static Node deleteLeafNodes(Node root) {

        // If the root is NULL, return NULL
        if (root == null) {
            return null;
        }

        // If the node itself is a leaf, delete it
        if (root.children.isEmpty()) {
            return null;
        }

        // Process children and remove
      	// any leaf nodes
        Iterator<Node> it = root.children.iterator();
        while (it.hasNext()) {
            Node child = it.next();
            if (child != null && child.children.isEmpty()) {
                it.remove();
            }
            else {
                deleteLeafNodes(child);
            }
        }

        return root;
    }

    // Recursive function for preorder traversal
    // of the N-ary tree
    static void preorderTraversal(Node root) {

        if (root == null) {
            return;
        }

        System.out.print(root.data + " ");
        for (Node child : root.children) {
            preorderTraversal(child);
        }
    }

    public static void main(String[] args) {

        // Representation of given N-ary tree
        //         1
        //       / | \
        //     2   3   4
        //    /         \
        //   5           6
        Node root = new Node(1);
        root.children.add(new Node(2));
        root.children.add(new Node(3));
        root.children.add(new Node(4));
        root.children.get(0).children.add(new Node(5));
        root.children.get(2).children.add(new Node(6));

        root = deleteLeafNodes(root);
        preorderTraversal(root);
    }
}