有bug

[75ACOL]

当我输入是 [1,null,10,12,13,4,6,null,15,null,null,5,11,null,2,14,7,null,8,null,null,null,9,3]这个报数组越界。
TreeNode treeNode = TreeUtils.mkTree("[1,null,10,12,13,4,6,null,15,null,null,5,11,null,2,14,7,null,8,null,null,null,9,3]");