input: Write a function to design a data structure in Python that can store integer values, add new values to the storage, and find the minimum value among the stored values. Implement this as a class called IntList with the methods `__init__`, `add_value`, and `find_min`.
  
  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
  assert IntList().add_value(5).find_min() == 5
  assert IntList().add_value(3).add_value(1).add_value(2).find_min() == 1
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