Given a list of lists of integers (nested list), flatten it into a single list containing all integers in order. For example, [[1, 2], [3, 4], [5]] should become [1, 2, 3, 4, 5].

Return an empty list for null or empty input.

Examples:

Input: nestedList = [[1, 2], [3, 4], [5]] Output: [1, 2, 3, 4, 5] Explanation: All integers from sublists combined into single list Input: nestedList = [[10], [20, 30], [40, 50, 60]] Output: [10, 20, 30, 40, 50, 60] Explanation: Flatten three sublists into one list Input: nestedList = null Output: [] Explanation: Null input returns empty list
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