Given a sorted list of unique integers, return the smallest sorted list of ranges that exactly covers all the numbers. Each range is formatted as 'a->b', or just 'a' when the range contains a single number (a == b). Return an empty list for null or empty input.

Examples:

Input: nums = [0, 1, 2, 4, 5, 7] Output: ['0->2', '4->5', '7'] Explanation: 0,1,2 form a consecutive range; 4,5 form a consecutive range; 7 stands alone. Input: nums = [0, 2, 3, 4, 6, 8, 9] Output: ['0', '2->4', '6', '8->9'] Explanation: 0 stands alone; 2,3,4 form a consecutive range; 6 stands alone; 8,9 form a consecutive range. Input: nums = [1] Output: ['1'] Explanation: A single element forms a range of just itself. Input: nums = [] Output: [] Explanation: Empty input returns an empty list. Input: nums = null Output: [] Explanation: Null input returns an empty list.
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