Given a Binary Search Tree (BST) with the root node `root`

, return the minimum difference between the values of any two different nodes in the tree.

**Example :**

Input:root = [4,2,6,1,3,null,null]Output:1Explanation:Note that root is a TreeNode object, not an array. The given tree [4,2,6,1,3,null,null] is represented by the following diagram: 4 / \ 2 6 / \ 1 3 while the minimum difference in this tree is 1, it occurs between node 1 and node 2, also between node 3 and node 2.

**Note:**

- The size of the BST will be between 2 and
`100`

. - The BST is always valid, each node's value is an integer, and each node's value is different.