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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def serialize(self, include_class=True, save_dynamic=False, **kwargs):
 """Serialize nested HasUID instances to a flat dictionary **Parameters**: * **include_class** - If True (the default), the name of the class will also be saved to the serialized dictionary under key :code:`'__class__'` * **save_dynamic** - If True, dynamic properties are written to the serialized dict (default: False). * You may also specify a **registry** - This is the flat dictionary where UID/HasUID pairs are stored. By default, no registry need be provided; a new dictionary will be created. * Any other keyword arguments will be passed through to the Property serializers. """

        registry = kwargs.pop('registry', None)
        if registry is None:
            registry = dict()
        if not registry:
            root = True
            registry.update({'__root__': self.uid})
        else:
            root = False
        key = self.uid
        if key not in registry:
            registry.update({key: None})
            registry.update({key: super(HasUID, self).serialize(
                registry=registry,
                include_class=include_class,
                save_dynamic=save_dynamic,
                **kwargs
            )})
        if root:
            return registry
        return key