input: Write a function to shuffle a list of numbers. If the given list is empty then return an empty list. If the function does not shuffle the list correctly for any input, then it should return None.
  assert shuffle_list([1, 2, 3, 4, 5]) != None
  assert shuffle_list([]) == []
  assert shuffle_list([2]) == [2]
  assert shuffle_list([1, 3, 5, 7, 9]) != None
output: def shuffle_list(nums):
      if not nums:
          return []
      shuffled = nums[:]
      import random
      random.shuffle(shuffled)
      if shuffled == nums:
          return None
      return shuffled