input: Write a python function to create a custom dictionary class with methods to get and set values.
  assert d.get('key1') == 'value1'
  assert d.get('key2') == 'value2'
  assert d.set('key3', 'value3') == None
  assert d.__repr__() == "{'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}"
output: class CustomDict:
      def __init__(self):
          self.data = {}
  
      def get(self, key):
          return self.data.get(key)
  
      def set(self, key, value):
          self.data[key] = value
  
      def __repr__(self):
          return repr(self.data)
  
  # Example usage
  d = CustomDict()
  d.set('key1', 'value1')
  d.set('key2', 'value2')
  d.set('key3', 'value3')