refactor: Getの返り値がnullにならないよう変更

server/usecase/channel_interactor.go

@@ -41,10 +41,14 @@ func (i *ChannelInteractor) GetAllChannels(ctx context.Context, userId uint64) (
 	channels, err := i.userRepository.FindChannelsByUserID(ctx, userId)
 	if err != nil {
 		if err == sql.ErrNoRows {
-			return &presenter.GetAllChannelsResponse{}, nil
+			return &presenter.GetAllChannelsResponse{
+				Channels: []*presenter.Channel{},
+			}, nil
 		}
 
-		return &presenter.GetAllChannelsResponse{}, err
+		return &presenter.GetAllChannelsResponse{
+			Channels: []*presenter.Channel{},
+		}, err
 	}
 
 	entitiedChannels := make([]*entity.Channel, len(channels))
@@ -58,7 +62,9 @@ func (i *ChannelInteractor) GetAllChannels(ctx context.Context, userId uint64) (
 func (i *ChannelInteractor) GetChannelByID(ctx context.Context, id uint64) (*presenter.GetChannelByIdResponse, error) {
 	channel, err := i.channelRepository.FindByID(ctx, id)
 	if err != nil {
-		return &presenter.GetChannelByIdResponse{}, err
+		return &presenter.GetChannelByIdResponse{
+			Channel: &presenter.ChannelDetail{},
+		}, err
 	}
 
 	return i.channelPresenter.GenerateGetChannelByIdResponse(channel.ToChannelEntity()), nil
@@ -67,7 +73,9 @@ func (i *ChannelInteractor) GetChannelByID(ctx context.Context, id uint64) (*pre
 func (i *ChannelInteractor) GetChannelsByName(ctx context.Context, name string) (*presenter.GetChannelsByNameResponse, error) {
 	channels, err := i.channelRepository.FindByName(ctx, name)
 	if err != nil {
-		return &presenter.GetChannelsByNameResponse{}, err
+		return &presenter.GetChannelsByNameResponse{
+			Channels: []*presenter.Channel{},
+		}, err
 	}
 
 	entitiedChannels := make([]*entity.Channel, len(channels))