Define a function that when passed two lists, each sorted in ascending order, returns a list that merges the two lists in an overall ascending order. Treat a null list as an empty list. Note: Python uses "None" instead of "null" merge([10, 70, 90], [20]) → [10, 20, 70, 90] merge([], [1, 2, 3, 4, 5, 6]) → [1, 2, 3, 4, 5, 6] merge([1, 2, 3, 4, 5, 6, 7, 8], []) → [1, 2, 3, 4, 5, 6, 7, 8]