input: Write a function to implement a class named IntList that stores integer values. The class should have a method to add a value to the list and another method to find the minimum value in the list. If the list is empty, return None.
  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
  
  assert IntList().find_min()==None
  list1 = IntList()
  list1.add_value(3)
  list1.add_value(5)
  list1.add_value(1)
  assert list1.find_min()==1
  list2 = IntList()
  list2.add_value(10)
  list2.add_value(2)
  assert list2.find_min()==2
  assert IntList().find_min()==None
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