input: Write a function to calculate the maximum, minimum, and mean of elements in a given string. Return these values as a tuple (max_element, min_element, mean_element). If the string is empty, return `(None, None, None)`.
  assert get_stats_for_string("abcdef") == ('f', 'a', 96.5)
  assert get_stats_for_string("12345") == ('5', '1', 3.0)
  assert get_stats_for_string("") == (None, None, None)
output: def get_stats_for_string(s):
      if not s:
          return (None, None, None)
      max_element = max(s)
      min_element = min(s)
      mean_element = sum(ord(c) for c in s) / len(s)
      return (max_element, min_element, mean_element)