the code is showing null pointer exception

Question

Given a Binary Search Tree and a node value X. Delete the node with the given value X from the BST. If no node with value x exists, then do not make any change.

class Tree {
  public static Node Inorder(Node root1) {
    while (root1.left != null) {
      root1 = root1.left;
    }
    return root1;
  }

  public static Node deleteNode(Node root, int x) {
    if (root.data > x) {
      root.left = deleteNode(root.left, x);
    } else if (root.data < x) {
      root.right = deleteNode(root.right, x);
    } else {
      if (root.left == null && root.right == null) return null;

      else if (root.left == null) return root.right;
      else if (root.right == null) return root.left;

      Node IS = Inorder(root.right);

      root.data = IS.data;
      root.right = deleteNode(root.right, IS.data);
    }

    return root;
  }
}