refactor(backend): remove unnecessary isNotNull sugar

22 files changed, 36 insertions, 65 deletions

diff --git a/packages/backend/src/core/AbuseReportNotificationService.ts b/packages/backend/src/core/AbuseReportNotificationService.ts
index df752afcd8..42e5931212 100644
--- a/packages/backend/src/core/AbuseReportNotificationService.ts
+++ b/packages/backend/src/core/AbuseReportNotificationService.ts
@@ -10,7 +10,6 @@ import sanitizeHtml from 'sanitize-html';
 import { DI } from '@/di-symbols.js';
 import { bindThis } from '@/decorators.js';
 import { GlobalEvents, GlobalEventService } from '@/core/GlobalEventService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import type {
 	AbuseReportNotificationRecipientRepository,
 	MiAbuseReportNotificationRecipient,
@@ -91,7 +90,7 @@ export class AbuseReportNotificationService implements OnApplicationShutdown {
 		const recipientEMailAddresses = await this.fetchEMailRecipients().then(it => it
 			.filter(it => it.isActive && it.userProfile?.emailVerified)
 			.map(it => it.userProfile?.email)
-			.filter(isNotNull),
+			.filter(x => x != null),
 		);
 
 		// 送信先の鮮度を保つため、毎回取得する
@@ -138,7 +137,7 @@ export class AbuseReportNotificationService implements OnApplicationShutdown {
 			.then(it => it
 				.filter(it => it.isActive && it.systemWebhookId && it.method === 'webhook')
 				.map(it => it.systemWebhookId)
-				.filter(isNotNull));
+				.filter(x => x != null));
 		for (const webhookId of recipientWebhookIds) {
 			await Promise.all(
 				abuseReports.map(it => {
@@ -340,7 +339,7 @@ export class AbuseReportNotificationService implements OnApplicationShutdown {
 	@bindThis
 	private async removeUnauthorizedRecipientUsers(recipients: MiAbuseReportNotificationRecipient[]): Promise<MiAbuseReportNotificationRecipient[]> {
 		const userRecipients = recipients.filter(it => it.userId !== null);
-		const recipientUserIds = new Set(userRecipients.map(it => it.userId).filter(isNotNull));
+		const recipientUserIds = new Set(userRecipients.map(it => it.userId).filter(x => x != null));
 		if (recipientUserIds.size <= 0) {
 			// ユーザが通知先として設定されていない場合、この関数での処理を行うべきレコードが無い
 			return recipients;
diff --git a/packages/backend/src/core/NoteCreateService.ts b/packages/backend/src/core/NoteCreateService.ts
index 0c9de117d2..a2c3aaa701 100644
--- a/packages/backend/src/core/NoteCreateService.ts
+++ b/packages/backend/src/core/NoteCreateService.ts
@@ -59,7 +59,6 @@ import { UtilityService } from '@/core/UtilityService.js';
 import { UserBlockingService } from '@/core/UserBlockingService.js';
 import { isReply } from '@/misc/is-reply.js';
 import { trackPromise } from '@/misc/promise-tracker.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { IdentifiableError } from '@/misc/identifiable-error.js';
 
 type NotificationType = 'reply' | 'renote' | 'quote' | 'mention';
@@ -839,7 +838,7 @@ export class NoteCreateService implements OnApplicationShutdown {
 		const mentions = extractMentions(tokens);
 		let mentionedUsers = (await Promise.all(mentions.map(m =>
 			this.remoteUserResolveService.resolveUser(m.username, m.host ?? user.host).catch(() => null),
-		))).filter(isNotNull);
+		))).filter(x => x != null);
 
 		// Drop duplicate users
 		mentionedUsers = mentionedUsers.filter((u, i, self) =>
diff --git a/packages/backend/src/core/activitypub/ApAudienceService.ts b/packages/backend/src/core/activitypub/ApAudienceService.ts
index 0fccc7b950..5a5a76f7d6 100644
--- a/packages/backend/src/core/activitypub/ApAudienceService.ts
+++ b/packages/backend/src/core/activitypub/ApAudienceService.ts
@@ -8,7 +8,6 @@ import promiseLimit from 'promise-limit';
 import type { MiRemoteUser, MiUser } from '@/models/User.js';
 import { concat, unique } from '@/misc/prelude/array.js';
 import { bindThis } from '@/decorators.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { getApIds } from './type.js';
 import { ApPersonService } from './models/ApPersonService.js';
 import type { ApObject } from './type.js';
@@ -41,7 +40,7 @@ export class ApAudienceService {
 		const limit = promiseLimit<MiUser | null>(2);
 		const mentionedUsers = (await Promise.all(
 			others.map(id => limit(() => this.apPersonService.resolvePerson(id, resolver).catch(() => null))),
-		)).filter(isNotNull);
+		)).filter(x => x != null);
 
 		if (toGroups.public.length > 0) {
 			return {
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index de3178b482..e2164fec1d 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -27,7 +27,6 @@ import { QueueService } from '@/core/QueueService.js';
 import type { UsersRepository, NotesRepository, FollowingsRepository, AbuseUserReportsRepository, FollowRequestsRepository } from '@/models/_.js';
 import { bindThis } from '@/decorators.js';
 import type { MiRemoteUser } from '@/models/User.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { GlobalEventService } from '@/core/GlobalEventService.js';
 import { AbuseReportService } from '@/core/AbuseReportService.js';
 import { getApHrefNullable, getApId, getApIds, getApType, isAccept, isActor, isAdd, isAnnounce, isBlock, isCollection, isCollectionOrOrderedCollection, isCreate, isDelete, isFlag, isFollow, isLike, isMove, isPost, isReject, isRemove, isTombstone, isUndo, isUpdate, validActor, validPost } from './type.js';
@@ -538,7 +537,7 @@ export class ApInboxService {
 		const userIds = uris
 			.filter(uri => uri.startsWith(this.config.url + '/users/'))
 			.map(uri => uri.split('/').at(-1))
-			.filter(isNotNull);
+			.filter(x => x != null);
 		const users = await this.usersRepository.findBy({
 			id: In(userIds),
 		});
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 4fc724b548..98e944f347 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -26,7 +26,6 @@ import type { MiUserKeypair } from '@/models/UserKeypair.js';
 import type { UsersRepository, UserProfilesRepository, NotesRepository, DriveFilesRepository, PollsRepository } from '@/models/_.js';
 import { bindThis } from '@/decorators.js';
 import { CustomEmojiService } from '@/core/CustomEmojiService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { IdService } from '@/core/IdService.js';
 import { JsonLdService } from './JsonLdService.js';
 import { ApMfmService } from './ApMfmService.js';
@@ -317,7 +316,7 @@ export class ApRendererService {
 		const getPromisedFiles = async (ids: string[]): Promise<MiDriveFile[]> => {
 			if (ids.length === 0) return [];
 			const items = await this.driveFilesRepository.findBy({ id: In(ids) });
-			return ids.map(id => items.find(item => item.id === id)).filter(isNotNull);
+			return ids.map(id => items.find(item => item.id === id)).filter(x => x != null);
 		};
 
 		let inReplyTo;
@@ -686,7 +685,7 @@ export class ApRendererService {
 		if (names.length === 0) return [];
 
 		const allEmojis = await this.customEmojiService.localEmojisCache.fetch();
-		const emojis = names.map(name => allEmojis.get(name)).filter(isNotNull);
+		const emojis = names.map(name => allEmojis.get(name)).filter(x => x != null);
 
 		return emojis;
 	}
diff --git a/packages/backend/src/core/activitypub/models/ApMentionService.ts b/packages/backend/src/core/activitypub/models/ApMentionService.ts
index 0ced7e88af..2cd151fa04 100644
--- a/packages/backend/src/core/activitypub/models/ApMentionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApMentionService.ts
@@ -8,7 +8,6 @@ import promiseLimit from 'promise-limit';
 import type { MiUser } from '@/models/_.js';
 import { toArray, unique } from '@/misc/prelude/array.js';
 import { bindThis } from '@/decorators.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { isMention } from '../type.js';
 import { Resolver } from '../ApResolverService.js';
 import { ApPersonService } from './ApPersonService.js';
@@ -28,7 +27,7 @@ export class ApMentionService {
 		const limit = promiseLimit<MiUser | null>(2);
 		const mentionedUsers = (await Promise.all(
 			hrefs.map(x => limit(() => this.apPersonService.resolvePerson(x, resolver).catch(() => null))),
-		)).filter(isNotNull);
+		)).filter(x => x != null);
 
 		return mentionedUsers;
 	}
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index c6e6b3a1e8..fc7aa1e0b9 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -24,7 +24,6 @@ import { UtilityService } from '@/core/UtilityService.js';
 import { bindThis } from '@/decorators.js';
 import { checkHttps } from '@/misc/check-https.js';
 import { IdentifiableError } from '@/misc/identifiable-error.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { getOneApId, getApId, getOneApHrefNullable, validPost, isEmoji, getApType } from '../type.js';
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApMfmService } from '../ApMfmService.js';
@@ -253,7 +252,7 @@ export class ApNoteService {
 				}
 			};
 
-			const uris = unique([note._misskey_quote, note.quoteUrl].filter(isNotNull));
+			const uris = unique([note._misskey_quote, note.quoteUrl].filter(x => x != null));
 			const results = await Promise.all(uris.map(tryResolveNote));
 
 			quote = results.filter((x): x is { status: 'ok', res: MiNote } => x.status === 'ok').map(x => x.res).at(0);
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index 744b1ea683..398c8695d2 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -38,7 +38,6 @@ import { MetaService } from '@/core/MetaService.js';
 import { DriveFileEntityService } from '@/core/entities/DriveFileEntityService.js';
 import type { AccountMoveService } from '@/core/AccountMoveService.js';
 import { checkHttps } from '@/misc/check-https.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { getApId, getApType, getOneApHrefNullable, isActor, isCollection, isCollectionOrOrderedCollection, isPropertyValue } from '../type.js';
 import { extractApHashtags } from './tag.js';
 import type { OnModuleInit } from '@nestjs/common';
@@ -637,7 +636,7 @@ export class ApPersonService implements OnModuleInit {
 
 			// とりあえずidを別の時間で生成して順番を維持
 			let td = 0;
-			for (const note of featuredNotes.filter(isNotNull)) {
+			for (const note of featuredNotes.filter(x => x != null)) {
 				td -= 1000;
 				transactionalEntityManager.insert(MiUserNotePining, {
 					id: this.idService.gen(Date.now() + td),
diff --git a/packages/backend/src/core/activitypub/models/ApQuestionService.ts b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
index d1936cfe1d..4fae1e897b 100644
--- a/packages/backend/src/core/activitypub/models/ApQuestionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
@@ -10,7 +10,6 @@ import type { Config } from '@/config.js';
 import type { IPoll } from '@/models/Poll.js';
 import type Logger from '@/logger.js';
 import { bindThis } from '@/decorators.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { isQuestion } from '../type.js';
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApResolverService } from '../ApResolverService.js';
@@ -52,7 +51,7 @@ export class ApQuestionService {
 
 		const choices = question[multiple ? 'anyOf' : 'oneOf']
 			?.map((x) => x.name)
-			.filter(isNotNull)
+			.filter(x => x != null)
 			?? [];
 
 		const votes = question[multiple ? 'anyOf' : 'oneOf']?.map((x) => x.replies?.totalItems ?? x._misskey_votes ?? 0);
diff --git a/packages/backend/src/core/activitypub/models/tag.ts b/packages/backend/src/core/activitypub/models/tag.ts
index e7ceec3262..f75cc45f7e 100644
--- a/packages/backend/src/core/activitypub/models/tag.ts
+++ b/packages/backend/src/core/activitypub/models/tag.ts
@@ -4,7 +4,6 @@
  */
 
 import { toArray } from '@/misc/prelude/array.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { isHashtag } from '../type.js';
 import type { IObject, IApHashtag } from '../type.js';
 
@@ -16,7 +15,7 @@ export function extractApHashtags(tags: IObject | IObject[] | null | undefined):
 	return hashtags.map(tag => {
 		const m = tag.name.match(/^#(.+)/);
 		return m ? m[1] : null;
-	}).filter(isNotNull);
+	}).filter(x => x != null);
 }
 
 export function extractApHashtagObjects(tags: IObject | IObject[] | null | undefined): IApHashtag[] {
diff --git a/packages/backend/src/core/entities/AbuseReportNotificationRecipientEntityService.ts b/packages/backend/src/core/entities/AbuseReportNotificationRecipientEntityService.ts
index 6819afafd9..1e23c194c5 100644
--- a/packages/backend/src/core/entities/AbuseReportNotificationRecipientEntityService.ts
+++ b/packages/backend/src/core/entities/AbuseReportNotificationRecipientEntityService.ts
@@ -11,7 +11,6 @@ import { bindThis } from '@/decorators.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { Packed } from '@/misc/json-schema.js';
 import { SystemWebhookEntityService } from '@/core/entities/SystemWebhookEntityService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 
 @Injectable()
 export class AbuseReportNotificationRecipientEntityService {
@@ -66,13 +65,13 @@ export class AbuseReportNotificationRecipientEntityService {
 			);
 		}
 
-		const userIds = objs.map(it => it.userId).filter(isNotNull);
+		const userIds = objs.map(it => it.userId).filter(x => x != null);
 		const users: Map<string, Packed<'UserLite'>> = (userIds.length > 0)
 			? await this.userEntityService.packMany(userIds)
 				.then(it => new Map(it.map(it => [it.id, it])))
 			: new Map();
 
-		const systemWebhookIds = objs.map(it => it.systemWebhookId).filter(isNotNull);
+		const systemWebhookIds = objs.map(it => it.systemWebhookId).filter(x => x != null);
 		const systemWebhooks: Map<string, Packed<'SystemWebhook'>> = (systemWebhookIds.length > 0)
 			? await this.systemWebhookEntityService.packMany(systemWebhookIds)
 				.then(it => new Map(it.map(it => [it.id, it])))
diff --git a/packages/backend/src/core/entities/AbuseUserReportEntityService.ts b/packages/backend/src/core/entities/AbuseUserReportEntityService.ts
index b0e1d1ab36..a13c244c19 100644
--- a/packages/backend/src/core/entities/AbuseUserReportEntityService.ts
+++ b/packages/backend/src/core/entities/AbuseUserReportEntityService.ts
@@ -10,7 +10,6 @@ import { awaitAll } from '@/misc/prelude/await-all.js';
 import type { MiAbuseUserReport } from '@/models/AbuseUserReport.js';
 import { bindThis } from '@/decorators.js';
 import { IdService } from '@/core/IdService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import type { Packed } from '@/misc/json-schema.js';
 import { UserEntityService } from './UserEntityService.js';
 
@@ -63,7 +62,7 @@ export class AbuseUserReportEntityService {
 	) {
 		const _reporters = reports.map(({ reporter, reporterId }) => reporter ?? reporterId);
 		const _targetUsers = reports.map(({ targetUser, targetUserId }) => targetUser ?? targetUserId);
-		const _assignees = reports.map(({ assignee, assigneeId }) => assignee ?? assigneeId).filter(isNotNull);
+		const _assignees = reports.map(({ assignee, assigneeId }) => assignee ?? assigneeId).filter(x => x != null);
 		const _userMap = await this.userEntityService.packMany(
 			[..._reporters, ..._targetUsers, ..._assignees],
 			null,
diff --git a/packages/backend/src/core/entities/DriveFileEntityService.ts b/packages/backend/src/core/entities/DriveFileEntityService.ts
index 02ff2e7754..c485555f90 100644
--- a/packages/backend/src/core/entities/DriveFileEntityService.ts
+++ b/packages/backend/src/core/entities/DriveFileEntityService.ts
@@ -16,7 +16,6 @@ import { appendQuery, query } from '@/misc/prelude/url.js';
 import { deepClone } from '@/misc/clone.js';
 import { bindThis } from '@/decorators.js';
 import { isMimeImage } from '@/misc/is-mime-image.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { IdService } from '@/core/IdService.js';
 import { UtilityService } from '../UtilityService.js';
 import { VideoProcessingService } from '../VideoProcessingService.js';
@@ -261,11 +260,11 @@ export class DriveFileEntityService {
 		files: MiDriveFile[],
 		options?: PackOptions,
 	): Promise<Packed<'DriveFile'>[]> {
-		const _user = files.map(({ user, userId }) => user ?? userId).filter(isNotNull);
+		const _user = files.map(({ user, userId }) => user ?? userId).filter(x => x != null);
 		const _userMap = await this.userEntityService.packMany(_user)
 			.then(users => new Map(users.map(user => [user.id, user])));
 		const items = await Promise.all(files.map(f => this.packNullable(f, options, f.userId ? { packedUser: _userMap.get(f.userId) } : {})));
-		return items.filter(isNotNull);
+		return items.filter(x => x != null);
 	}
 
 	@bindThis
@@ -290,6 +289,6 @@ export class DriveFileEntityService {
 	): Promise<Packed<'DriveFile'>[]> {
 		if (fileIds.length === 0) return [];
 		const filesMap = await this.packManyByIdsMap(fileIds, options);
-		return fileIds.map(id => filesMap.get(id)).filter(isNotNull);
+		return fileIds.map(id => filesMap.get(id)).filter(x => x != null);
 	}
 }
diff --git a/packages/backend/src/core/entities/InviteCodeEntityService.ts b/packages/backend/src/core/entities/InviteCodeEntityService.ts
index 26f57e1299..5d3e823a2a 100644
--- a/packages/backend/src/core/entities/InviteCodeEntityService.ts
+++ b/packages/backend/src/core/entities/InviteCodeEntityService.ts
@@ -12,7 +12,6 @@ import type { MiUser } from '@/models/User.js';
 import type { MiRegistrationTicket } from '@/models/RegistrationTicket.js';
 import { bindThis } from '@/decorators.js';
 import { IdService } from '@/core/IdService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { UserEntityService } from './UserEntityService.js';
 
 @Injectable()
@@ -59,8 +58,8 @@ export class InviteCodeEntityService {
 		tickets: MiRegistrationTicket[],
 		me: { id: MiUser['id'] },
 	) {
-		const _createdBys = tickets.map(({ createdBy, createdById }) => createdBy ?? createdById).filter(isNotNull);
-		const _usedBys = tickets.map(({ usedBy, usedById }) => usedBy ?? usedById).filter(isNotNull);
+		const _createdBys = tickets.map(({ createdBy, createdById }) => createdBy ?? createdById).filter(x => x != null);
+		const _usedBys = tickets.map(({ usedBy, usedById }) => usedBy ?? usedById).filter(x => x != null);
 		const _userMap = await this.userEntityService.packMany([..._createdBys, ..._usedBys], me)
 			.then(users => new Map(users.map(u => [u.id, u])));
 		return Promise.all(
diff --git a/packages/backend/src/core/entities/NoteEntityService.ts b/packages/backend/src/core/entities/NoteEntityService.ts
index 2ce72c50b8..2cd092231c 100644
--- a/packages/backend/src/core/entities/NoteEntityService.ts
+++ b/packages/backend/src/core/entities/NoteEntityService.ts
@@ -14,7 +14,6 @@ import type { MiNote } from '@/models/Note.js';
 import type { MiNoteReaction } from '@/models/NoteReaction.js';
 import type { UsersRepository, NotesRepository, FollowingsRepository, PollsRepository, PollVotesRepository, NoteReactionsRepository, ChannelsRepository } from '@/models/_.js';
 import { bindThis } from '@/decorators.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { DebounceLoader } from '@/misc/loader.js';
 import { IdService } from '@/core/IdService.js';
 import type { OnModuleInit } from '@nestjs/common';
@@ -276,7 +275,7 @@ export class NoteEntityService implements OnModuleInit {
 				packedFiles.set(k, v);
 			}
 		}
-		return fileIds.map(id => packedFiles.get(id)).filter(isNotNull);
+		return fileIds.map(id => packedFiles.get(id)).filter(x => x != null);
 	}
 
 	@bindThis
@@ -449,12 +448,12 @@ export class NoteEntityService implements OnModuleInit {
 
 		await this.customEmojiService.prefetchEmojis(this.aggregateNoteEmojis(notes));
 		// TODO: 本当は renote とか reply がないのに renoteId とか replyId があったらここで解決しておく
-		const fileIds = notes.map(n => [n.fileIds, n.renote?.fileIds, n.reply?.fileIds]).flat(2).filter(isNotNull);
+		const fileIds = notes.map(n => [n.fileIds, n.renote?.fileIds, n.reply?.fileIds]).flat(2).filter(x => x != null);
 		const packedFiles = fileIds.length > 0 ? await this.driveFileEntityService.packManyByIdsMap(fileIds) : new Map();
 		const users = [
 			...notes.map(({ user, userId }) => user ?? userId),
-			...notes.map(({ replyUserId }) => replyUserId).filter(isNotNull),
-			...notes.map(({ renoteUserId }) => renoteUserId).filter(isNotNull),
+			...notes.map(({ replyUserId }) => replyUserId).filter(x => x != null),
+			...notes.map(({ renoteUserId }) => renoteUserId).filter(x => x != null),
 		];
 		const packedUsers = await this.userEntityService.packMany(users, me)
 			.then(users => new Map(users.map(u => [u.id, u])));
diff --git a/packages/backend/src/core/entities/NotificationEntityService.ts b/packages/backend/src/core/entities/NotificationEntityService.ts
index 94d56c883b..f393513510 100644
--- a/packages/backend/src/core/entities/NotificationEntityService.ts
+++ b/packages/backend/src/core/entities/NotificationEntityService.ts
@@ -13,7 +13,6 @@ import type { MiGroupedNotification, MiNotification } from '@/models/Notificatio
 import type { MiNote } from '@/models/Note.js';
 import type { Packed } from '@/misc/json-schema.js';
 import { bindThis } from '@/decorators.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { FilterUnionByProperty, groupedNotificationTypes } from '@/types.js';
 import { CacheService } from '@/core/CacheService.js';
 import { RoleEntityService } from './RoleEntityService.js';
@@ -103,7 +102,7 @@ export class NotificationEntityService implements OnModuleInit {
 					user,
 					reaction: reaction.reaction,
 				};
-			}))).filter(r => isNotNull(r.user));
+			}))).filter(r => r.user != null);
 			// if all users have been deleted, don't show this notification
 			if (reactions.length === 0) {
 				return null;
@@ -124,7 +123,7 @@ export class NotificationEntityService implements OnModuleInit {
 				}
 
 				return this.userEntityService.pack(userId, { id: meId });
-			}))).filter(isNotNull);
+			}))).filter(x => x != null);
 			// if all users have been deleted, don't show this notification
 			if (users.length === 0) {
 				return null;
@@ -181,7 +180,7 @@ export class NotificationEntityService implements OnModuleInit {
 
 		validNotifications = await this.#filterValidNotifier(validNotifications, meId);
 
-		const noteIds = validNotifications.map(x => 'noteId' in x ? x.noteId : null).filter(isNotNull);
+		const noteIds = validNotifications.map(x => 'noteId' in x ? x.noteId : null).filter(x => x != null);
 		const notes = noteIds.length > 0 ? await this.notesRepository.find({
 			where: { id: In(noteIds) },
 			relations: ['user', 'reply', 'reply.user', 'renote', 'renote.user'],
@@ -223,7 +222,7 @@ export class NotificationEntityService implements OnModuleInit {
 			);
 		});
 
-		return (await Promise.all(packPromises)).filter(isNotNull);
+		return (await Promise.all(packPromises)).filter(x => x != null);
 	}
 
 	@bindThis
@@ -305,7 +304,7 @@ export class NotificationEntityService implements OnModuleInit {
 			this.cacheService.userProfileCache.fetch(meId).then(p => new Set(p.mutedInstances)),
 		]);
 
-		const notifierIds = notifications.map(notification => 'notifierId' in notification ? notification.notifierId : null).filter(isNotNull);
+		const notifierIds = notifications.map(notification => 'notifierId' in notification ? notification.notifierId : null).filter(x => x != null);
 		const notifiers = notifierIds.length > 0 ? await this.usersRepository.find({
 			where: { id: In(notifierIds) },
 		}) : [];
@@ -313,7 +312,7 @@ export class NotificationEntityService implements OnModuleInit {
 		const filteredNotifications = ((await Promise.all(notifications.map(async (notification) => {
 			const isValid = this.#validateNotifier(notification, userIdsWhoMeMuting, userMutedInstances, notifiers);
 			return isValid ? notification : null;
-		}))) as [T | null] ).filter(isNotNull);
+		}))) as [T | null] ).filter(x => x != null);
 
 		return filteredNotifications;
 	}
diff --git a/packages/backend/src/core/entities/PageEntityService.ts b/packages/backend/src/core/entities/PageEntityService.ts
index 142d9e81db..46bf51bb6d 100644
--- a/packages/backend/src/core/entities/PageEntityService.ts
+++ b/packages/backend/src/core/entities/PageEntityService.ts
@@ -14,7 +14,6 @@ import type { MiPage } from '@/models/Page.js';
 import type { MiDriveFile } from '@/models/DriveFile.js';
 import { bindThis } from '@/decorators.js';
 import { IdService } from '@/core/IdService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import { UserEntityService } from './UserEntityService.js';
 import { DriveFileEntityService } from './DriveFileEntityService.js';
 
@@ -106,7 +105,7 @@ export class PageEntityService {
 			script: page.script,
 			eyeCatchingImageId: page.eyeCatchingImageId,
 			eyeCatchingImage: page.eyeCatchingImageId ? await this.driveFileEntityService.pack(page.eyeCatchingImageId) : null,
-			attachedFiles: this.driveFileEntityService.packMany((await Promise.all(attachedFiles)).filter(isNotNull)),
+			attachedFiles: this.driveFileEntityService.packMany((await Promise.all(attachedFiles)).filter(x => x != null)),
 			likedCount: page.likedCount,
 			isLiked: meId ? await this.pageLikesRepository.exists({ where: { pageId: page.id, userId: meId } }) : undefined,
 		});
diff --git a/packages/backend/src/core/entities/UserEntityService.ts b/packages/backend/src/core/entities/UserEntityService.ts
index b80a1ec206..da96878713 100644
--- a/packages/backend/src/core/entities/UserEntityService.ts
+++ b/packages/backend/src/core/entities/UserEntityService.ts
@@ -47,7 +47,6 @@ import { IdService } from '@/core/IdService.js';
 import type { AnnouncementService } from '@/core/AnnouncementService.js';
 import type { CustomEmojiService } from '@/core/CustomEmojiService.js';
 import { AvatarDecorationService } from '@/core/AvatarDecorationService.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 import type { OnModuleInit } from '@nestjs/common';
 import type { NoteEntityService } from './NoteEntityService.js';
 import type { DriveFileEntityService } from './DriveFileEntityService.js';
@@ -514,7 +513,7 @@ export class UserEntityService implements OnModuleInit {
 				movedTo: user.movedToUri ? this.apPersonService.resolvePerson(user.movedToUri).then(user => user.id).catch(() => null) : null,
 				alsoKnownAs: user.alsoKnownAs
 					? Promise.all(user.alsoKnownAs.map(uri => this.apPersonService.fetchPerson(uri).then(user => user?.id).catch(() => null)))
-						.then(xs => xs.length === 0 ? null : xs.filter(isNotNull))
+						.then(xs => xs.length === 0 ? null : xs.filter(x => x != null))
 					: null,
 				createdAt: this.idService.parse(user.id).date.toISOString(),
 				updatedAt: user.updatedAt ? user.updatedAt.toISOString() : null,
diff --git a/packages/backend/src/misc/is-not-null.ts b/packages/backend/src/misc/is-not-null.ts
deleted file mode 100644
index 8d9dc8bb39..0000000000
--- a/packages/backend/src/misc/is-not-null.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-export function isNotNull<T extends NonNullable<unknown>>(input: T | undefined | null): input is T {
-	return input != null;
-}
diff --git a/packages/backend/src/server/api/endpoints/gallery/posts/create.ts b/packages/backend/src/server/api/endpoints/gallery/posts/create.ts
index 46f8998810..504a9c789e 100644
--- a/packages/backend/src/server/api/endpoints/gallery/posts/create.ts
+++ b/packages/backend/src/server/api/endpoints/gallery/posts/create.ts
@@ -12,7 +12,6 @@ import type { MiDriveFile } from '@/models/DriveFile.js';
 import { IdService } from '@/core/IdService.js';
 import { GalleryPostEntityService } from '@/core/entities/GalleryPostEntityService.js';
 import { DI } from '@/di-symbols.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 
 export const meta = {
 	tags: ['gallery'],
@@ -70,7 +69,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 					id: fileId,
 					userId: me.id,
 				}),
-			))).filter(isNotNull);
+			))).filter(x => x != null);
 
 			if (files.length === 0) {
 				throw new Error();
diff --git a/packages/backend/src/server/api/endpoints/gallery/posts/update.ts b/packages/backend/src/server/api/endpoints/gallery/posts/update.ts
index 8bd83ff5ba..2f977784ec 100644
--- a/packages/backend/src/server/api/endpoints/gallery/posts/update.ts
+++ b/packages/backend/src/server/api/endpoints/gallery/posts/update.ts
@@ -10,7 +10,6 @@ import type { DriveFilesRepository, GalleryPostsRepository } from '@/models/_.js
 import type { MiDriveFile } from '@/models/DriveFile.js';
 import { GalleryPostEntityService } from '@/core/entities/GalleryPostEntityService.js';
 import { DI } from '@/di-symbols.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 
 export const meta = {
 	tags: ['gallery'],
@@ -68,7 +67,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 					id: fileId,
 					userId: me.id,
 				}),
-			))).filter(isNotNull);
+			))).filter(x => x != null);
 
 			if (files.length === 0) {
 				throw new Error();
diff --git a/packages/backend/src/server/api/endpoints/pinned-users.ts b/packages/backend/src/server/api/endpoints/pinned-users.ts
index 784766bcb5..15832ef7f8 100644
--- a/packages/backend/src/server/api/endpoints/pinned-users.ts
+++ b/packages/backend/src/server/api/endpoints/pinned-users.ts
@@ -12,7 +12,6 @@ import { Endpoint } from '@/server/api/endpoint-base.js';
 import { MetaService } from '@/core/MetaService.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { DI } from '@/di-symbols.js';
-import { isNotNull } from '@/misc/is-not-null.js';
 
 export const meta = {
 	tags: ['users'],
@@ -53,7 +52,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				host: acct.host ?? IsNull(),
 			})));
 
-			return await this.userEntityService.packMany(users.filter(isNotNull), me, { schema: 'UserDetailed' });
+			return await this.userEntityService.packMany(users.filter(x => x != null), me, { schema: 'UserDetailed' });
 		});
 	}
 }