fix(pubsub): fix issue preventing clearing BQ subscription (#8040)

* fix(pubsub): allow clearing of bq subscriptions

* update behavior in fake as well

pubsub/pstest/fake.go

@@ -605,9 +605,15 @@ func (s *GServer) UpdateSubscription(_ context.Context, req *pb.UpdateSubscripti
 			sub.proto.PushConfig = req.Subscription.PushConfig
 
 		case "bigquery_config":
+			// If bq config is nil here, it will have been cleared.
+			// Otherwise, we'll consider the subscription active if any table is set.
 			sub.proto.BigqueryConfig = req.GetSubscription().GetBigqueryConfig()
-			if sub.proto.GetBigqueryConfig().GetTable() != "" {
-				sub.proto.GetBigqueryConfig().State = pb.BigQueryConfig_ACTIVE
+			if sub.proto.GetBigqueryConfig() != nil {
+				if sub.proto.GetBigqueryConfig().GetTable() != "" {
+					sub.proto.BigqueryConfig.State = pb.BigQueryConfig_ACTIVE
+				} else {
+					return nil, status.Errorf(codes.InvalidArgument, "table must be provided")
+				}
 			}
 
 		case "ack_deadline_seconds":

pubsub/subscription.go

@@ -265,6 +265,11 @@ func (bc *BigQueryConfig) toProto() *pb.BigQueryConfig {
 	if bc == nil {
 		return nil
 	}
+	// If the config is zero valued, this is the sentinel for
+	// clearing bigquery config and switch back to pull.
+	if *bc == (BigQueryConfig{}) {
+		return nil
+	}
 	pbCfg := &pb.BigQueryConfig{
 		Table:             bc.Table,
 		UseTopicSchema:    bc.UseTopicSchema,