```
# Definition for a binary tree node
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
# @param root, a tree node
# @return a list of integers
def rightSideView(self, root):
if root == None:
return []
result, current_level = [], [root]
while current_level:
next_level = []
for i in range(len(current_level)):
node = current_level.pop(0)
if i == 0:
result.append(node.val)
if node.right:
next_level.append(node.right)
if node.left:
next_level.append(node.left)
current_level = next_level
return result
```

I've tried different ways of implementing this, but all end up with the same Runtime Error

```
ValueError: Expecting property name: line 1 column 2 (char 1)
```

anybody knows what's wrong? Thanks!