input: Write a class named IntList to store integer values in Python. The class should have a constructor that initializes an empty list to store values. The class should also have methods to add integer values to the list and to find the minimum value in the list.
  
  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().add_value(5).add_value(3).add_value(8).find_min() == 3
  assert IntList().add_value(-1).add_value(-5).add_value(0).find_min() == -5
  assert IntList().add_value(10).find_min() == 10
  assert IntList().find_min() == None
output: class IntList:
      def __init__(self):
          self.values = []
     
      def add_value(self, value):
          self.values.append(value)
          return self
      
      def find_min(self):
          return min(self.values) if self.values else None