more nullability

src/objective-c/GRPCClient/GRPCCallOptions.h

@@ -64,7 +64,7 @@ typedef NS_ENUM(NSUInteger, GRPCTransportType) {
  * This method is called when gRPC is about to start the call. When OAuth token is acquired,
  * \a handler is expected to be called with \a token being the new token to be used for this call.
  */
-- (void)getTokenWithHandler:(void (^)(NSString *token))handler;
+- (void)getTokenWithHandler:(void (^)(NSString * _Nullable token))handler;
 @end
 
 @interface GRPCCallOptions : NSObject<NSCopying, NSMutableCopying>

src/objective-c/tests/APIv2Tests/APIv2Tests.m

@@ -93,8 +93,7 @@ static const NSTimeInterval kTestTimeout = 16;
   }
 }
 
-- (void)closedWithTrailingMetadata:(NSDictionary *)trailingMetadata
+- (void)closedWithTrailingMetadata:(NSDictionary *)trailingMetadata error:(NSError *)error {
-                             error:(NSError *)error {
   if (self->_closeCallback) {
     self->_closeCallback(trailingMetadata, error);
   }