input: Write a function to check if a list of integer values can be stored in the designed data structure and return the minimum value stored in it. If the list is empty, return None.
  def use_int_list(values):
      int_list = IntList()
      for value in values:
          int_list.add_value(value)
      return int_list.find_min() if values else None
  assert use_int_list([3, 8, 2, 5]) == 2
  assert use_int_list([10, -1, 7, 6]) == -1
  assert use_int_list([9]) == 9
  assert use_int_list([]) == None
output: def use_int_list(values):
      int_list = IntList()
      for value in values:
          int_list.add_value(value)
      return int_list.find_min() if values else None