input: Write a function to find the mode of a given set of values. The mode is the value that appears most frequently in the set. If there are multiple modes, return any one of them. If the set is empty, return None.
  assert find_mode([1, 2, 3, 2, 4, 2]) == 2
  assert find_mode([3, 5, 2, 3, 1, 3]) == 3
  assert find_mode([4, 3, 1, 2]) == 4  # or any of 3, 1, 2
  assert find_mode([]) == None
output: def find_mode(values):
      if not values:
          return None
      count_dict = {}
      for value in values:
          if value in count_dict:
              count_dict[value] += 1
          else:
              count_dict[value] = 1
      max_count = max(count_dict.values())
      for value, count in count_dict.items():
          if count == max_count:
              return value