Return empty in slam servicer

SlamController/slam_servicer.py

@@ -1,4 +1,5 @@
-import SlamController_pb2_grpc 
+import SlamController_pb2_grpc
+import SlamController_pb2
 import slam_streamer as slam
 from threading import Thread
 
@@ -17,7 +18,9 @@ class SlamServicer(SlamController_pb2_grpc.SlamControlServicer):
             self.slam.map_meters = request.map_size_meters
             self.slam_thread = Thread(target=self.slam.start)
             self.slam_thread.start()
+        return SlamController_pb2.Empty()
 
     def stop_streaming(self, request, context):
         if self.slam_thread is not None:
-            self.slam.stop_scanning()
+            self.slam.stop_scanning()
+        return SlamController_pb2.Empty()