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.
  assert find_mode([1, 2, 3, 2, 4, 2]) == 2
  assert find_mode([1, 3, 3, 2, 4, 2]) == 3
  assert find_mode([1, 2, 3, 4, 5]) == 1
  assert find_mode([]) == None
output: def find_mode(values):
      if not values:
          return None
      freq = {}
      for value in values:
          if value in freq:
              freq[value] += 1
          else:
              freq[value] = 1
      max_freq = max(freq.values())
      for value, count in freq.items():
          if count == max_freq:
              return value