Change exception type to AssertError
diff --git a/src/python/grpcio/grpc/_server.py b/src/python/grpcio/grpc/_server.py
index 0421457..2761022 100644
--- a/src/python/grpcio/grpc/_server.py
+++ b/src/python/grpcio/grpc/_server.py
@@ -329,7 +329,8 @@
             request = self._state.request
             self._state.request = None
             return request
-        raise Exception('gRPC Error: Invalid _state')
+
+        raise AssertionError()  # should never run
 
     def _next(self):
         with self._state.condition: