human
Solve the following python programming problem given the following code:
def closestKValues(self, root, target, k) : 
    '
        :type root: TreeNode
        :type target: float
        :type k: int
        :rtype: List[int]
        ' 
    def nextNode(stack, child1, child2) : 
        if stack : 
            if child2 (stack) : 
                stack.append (child2 (stack)) 
                while child1 (stack) : 
                    stack.append (child1 (stack)) 
else : 
                child = stack.pop () 
                while (stack and (child is child2 (stack))) : 
                    child = stack.pop () 
backward = (lambda stack : stack [(- 1)].left) 
    forward = (lambda stack : stack [(- 1)].right) 
    stack = [] 
    while root : 
        stack.append (root) 
        root = (root.left if (target < root.val) else root.right) 
dist = (lambda node : abs ((node.val - target))) 
    forward_stack = stack [: (stack.index (min (stack, key = dist)) + 1)] 
    backward_stack = list (forward_stack) 
    nextNode (backward_stack, backward, forward) 
    result = [] 
    for _ in xrange (k) : 
        if (forward_stack and ((not backward_stack) or (dist (forward_stack [(- 1)]) < dist (backward_stack [(- 1)])))) : 
            result.append (forward_stack [(- 1)].val) 
            nextNode (forward_stack, _, backward) 
else : 
            if (backward_stack and ((not forward_stack) or (dist (backward_stack [(- 1)]) <= dist (forward_stack [(- 1)])))) : 
                result.append (backward_stack [(- 1)].val) 
                nextNode (backward_stack, backward, forward) 
return result 

    
    

    Fix the buggy line: nextNode (forward_stack, _, backward)
assistant
#Here is Python code to fix the buggy line: nextNode (forward_stack, _, backward)
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nextNode (forward_stack, forward, backward)