input: Write a function to calculate the maximum, minimum, and mean number of elements in a given string. Return the results as a tuple containing the maximum, minimum, and mean values. If the string is empty, return `None`.
  
  def get_stats_for_string(string):
      if not string:
          return None
      num_elements = len(string)
      max_element = max(string)
      min_element = min(string)
      mean_element = sum(ord(char) for char in string) / num_elements
      return (max_element, min_element, mean_element)
  
  assert get_stats_for_string("abcdef")==('f', 'a', 99.5)
  assert get_stats_for_string("Hello")==('o', 'H', 100.4)
  assert get_stats_for_string("")==None
  assert get_stats_for_string("A")==('A', 'A', 65.0)
  assert get_stats_for_string("12345")==('5', '1', 53.0)
output: def get_stats_for_string(string):
      if not string:
          return None
      num_elements = len(string)
      max_element = max(string)
      min_element = min(string)
      mean_element = sum(ord(char) for char in string) / num_elements
      return (max_element, min_element, mean_element)