Typo error in Ruby CS - Recursion

Link: https://www.codequizzes.com/computer-science/beginner/recursion

There's a typo error in the answer for:
Question: Define a recursive function that flattens an array. The method should convert [[1, 2], [3, 4]] to [1, 2, 3, 4] and [[1, [8, 9]], [3, 4]] to [1, 8, 9, 3, 4].

Answer: Line 3 is if element.kind_of?(Array, it is missing closing bracket. Either use if element.kind_of?(Array) or if element.kind_of? Array