input: Write a function to find and return the median of an unsorted list of numbers. Implement the function by sorting the list and then calculating the median.
  assert find_median([3, 9, 2, 11, 5]) == 5
  assert find_median([4, 1, 5, 7, 9, 6]) == 5.5
  assert find_median([5, 3, 3, 2, 1]) == 3
  assert find_median([1, 2, 3, 4, 5]) == 3
  assert find_median([]) == None
output: def find_median(nums):
      if not nums:
          return None
      nums.sort()
      n = len(nums)
      if n % 2 == 1:
          return nums[n // 2]
      else:
          return (nums[n // 2 - 1] + nums[n // 2]) / 2