以下代码能够正确统计二叉树中叶子结点的数量。（ ）

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def count_leaf(root):
    if not root:
        return 0
    if not root.left and not root.right:
        return 1
    return count_leaf(root.left) + count_leaf(root.right)

if __name__ == "__main__":
    root1 = TreeNode(1)
    root1.left = TreeNode(2)
    root1.right = TreeNode(3)
    root1.left.left = TreeNode(4)
    root1.left.right = TreeNode(5)
    root1.right.right = TreeNode(6)
    print(f"二叉树1的叶子节点数：{count_leaf(root1)}")
    root2 = TreeNode(1)
    print(f"二叉树2的叶子节点数：{count_leaf(root2)}") 1

    root3 = None
    print(f"空树的叶子节点数：{count_leaf(root3)}")