input: Write a function to create a data structure that can store integer values, with methods to add a new value and find the minimum value among the stored values. The data structure should be named IntList.
  class IntList:
      def __init__(self):
          self.values = []
     
      def add_value(self, value):
          self.values.append(value)
      
      def find_min(self):
          return min(self.values)
  
  assert IntList().find_min() == None
  int_list = IntList()
  int_list.add_value(5)
  int_list.add_value(3)
  int_list.add_value(10)
  assert int_list.find_min() == 3
  int_list.add_value(1)
  assert int_list.find_min() == 1
output: 
  class IntList:
      def __init__(self):
          self.values = []
     
      def add_value(self, value):
          self.values.append(value)
      
      def find_min(self):
          return min(self.values) if self.values else None
  