def __init__(self,request_adapter: RequestAdapter, backing_store: Optional[BackingStoreFactory] = None) -> None:
        """
        Instantiates a new BaseGraphServiceClient and sets the default values.
        param backing_store: The backing store to use for the models.
        param request_adapter: The request adapter to use to execute the requests.
        Returns: None
        """
        if request_adapter is None:
            raise TypeError("request_adapter cannot be null.")
        super().__init__(request_adapter, "{+baseurl}", None)
        register_default_serializer(JsonSerializationWriterFactory)
        register_default_serializer(TextSerializationWriterFactory)
        register_default_serializer(FormSerializationWriterFactory)
        register_default_serializer(MultipartSerializationWriterFactory)
        register_default_deserializer(JsonParseNodeFactory)
        register_default_deserializer(TextParseNodeFactory)
        register_default_deserializer(FormParseNodeFactory)
        if not self.request_adapter.base_url:
            self.request_adapter.base_url = "https://graph.microsoft.com/v1.0"
        self.path_parameters["base_url"] = self.request_adapter.base_url
        self.request_adapter.enable_backing_store(backing_store)

        Instantiates a new BaseGraphServiceClient and sets the default values.
        param backing_store: The backing store to use for the models.
        param request_adapter: The request adapter to use to execute the requests.
        Returns: None
        
msgraph/generated/base_graph_service_client.py