input: Write a function to create a data structure in Python that stores integer values, allows adding values, and can find the minimum value among the stored integers. The function should return the data structure with specified methods.
  assert create_int_list().add_value(5).add_value(3).add_value(8).find_min()==3
  assert create_int_list().add_value(10).add_value(2).add_value(7).find_min()==2
  assert create_int_list().find_min()==None
output: def create_int_list():
      class IntList:
          def __init__(self):
              self.values = []
          
          def add_value(self, value):
              self.values.append(value)
              return self
          
          def find_min(self):
              if not self.values:
                  return None
              return min(self.values)
      
      return IntList()