Add missing metadata TypeError case

Code formatted.

src/python/grpcio/grpc/experimental/aio/_base_call.py

@@ -23,8 +23,7 @@ from typing import AsyncIterable, Awaitable, Generic, Optional, Union
 
 import grpc
 
-from ._typing import (DoneCallbackType, EOFType, RequestType,
-                      ResponseType)
+from ._typing import (DoneCallbackType, EOFType, RequestType, ResponseType)
 from ._metadata import Metadata
 
 __all__ = 'RpcContext', 'Call', 'UnaryUnaryCall', 'UnaryStreamCall'

src/python/grpcio/grpc/experimental/aio/_base_server.py

@@ -158,8 +158,7 @@ class ServicerContext(Generic[RequestType, ResponseType], abc.ABC):
         """
 
     @abc.abstractmethod
-    async def send_initial_metadata(self,
-                                    initial_metadata: Metadata) -> None:
+    async def send_initial_metadata(self, initial_metadata: Metadata) -> None:
         """Sends the initial metadata value to the client.
 
         This method need not be called by implementations if they have no
@@ -191,8 +190,7 @@ class ServicerContext(Generic[RequestType, ResponseType], abc.ABC):
         """
 
     @abc.abstractmethod
-    async def set_trailing_metadata(self,
-                                    trailing_metadata: Metadata) -> None:
+    async def set_trailing_metadata(self, trailing_metadata: Metadata) -> None:
         """Sends the trailing metadata for the RPC.
 
         This method need not be called by implementations if they have no

src/python/grpcio/grpc/experimental/aio/_interceptor.py

@@ -27,8 +27,8 @@ from ._call import _RPC_ALREADY_FINISHED_DETAILS, _RPC_HALF_CLOSED_DETAILS
 from ._call import _API_STYLE_ERROR
 from ._utils import _timeout_to_deadline
 from ._typing import (RequestType, SerializingFunction, DeserializingFunction,
-                      ResponseType, DoneCallbackType,
-                      RequestIterableType, ResponseIterableType)
+                      ResponseType, DoneCallbackType, RequestIterableType,
+                      ResponseIterableType)
 from ._metadata import Metadata
 
 _LOCAL_CANCELLATION_DETAILS = 'Locally cancelled by application!'

src/python/grpcio_tests/tests_aio/unit/metadata_test.py

@@ -65,6 +65,10 @@ _INVALID_METADATA_TEST_CASES = (
         TypeError,
         ((None, {}),),
     ),
+    (
+        TypeError,
+        (({}, {}),),
+    ),
     (
         TypeError,
         (('normal', object()),),