input: Write a function to create a class in Python that stores integer values and provides methods to add values and find the minimum value in the list of stored values. If the list is empty, the find_min method should 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
  list_obj = IntList()
  list_obj.add_value(3)
  list_obj.add_value(1)
  list_obj.add_value(4)
  assert list_obj.find_min()==1
  empty_list_obj = IntList()
  assert empty_list_obj.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
  