missing nil check for grpc WaitGroup

server/grpc/subscriber.go

@@ -231,9 +231,13 @@ func (g *grpcServer) createSubHandler(sb *subscriber, opts server.Options) broke
 				fn = opts.SubWrappers[i-1](fn)
 			}
 
+			if g.wg != nil {
 				g.wg.Add(1)
+			}
 			go func() {
+				if g.wg != nil {
 					defer g.wg.Done()
+				}
 				fn(ctx, &rpcMessage{
 					topic:       sb.topic,
 					contentType: ct,