refactor(backend): 存在確認のfindOneByをexistに置き換え (#11224)

* refactor(backend): 存在確認の`findOneBy`を`exist`に置き換え

* cleanup

packages/backend/src/server/api/endpoints/users/following.ts

@@ -97,11 +97,13 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 				if (me == null) {
 					throw new ApiError(meta.errors.forbidden);
 				} else if (me.id !== user.id) {
-					const following = await this.followingsRepository.findOneBy({
-						followeeId: user.id,
-						followerId: me.id,
+					const isFollowing = await this.followingsRepository.exist({
+						where: {
+							followeeId: user.id,
+							followerId: me.id,
+						},
 					});
-					if (following == null) {
+					if (!isFollowing) {
 						throw new ApiError(meta.errors.forbidden);
 					}
 				}