input: Write a python function to handle `RelatedManagerListSerializerField` and test its `set_value` method.
  assert isinstance(RelatedManagerListSerializerField(None).set_value(None), type(None))
  assert isinstance(RelatedManagerListSerializerField(None).set_value([]), type(None))
  assert isinstance(RelatedManagerListSerializerField(None).set_value('not an iterable'), type(None))
output: def RelatedManagerListSerializerField(value):
      class MockRelatedManagerListSerializerField:
          def __init__(self, value):
              self.value = value
          
          def set_value(self, value):
              self.value = value
              return None
      
      return MockRelatedManagerListSerializerField(value)