diff --git a/packages/backend/src/core/activitypub/models/ApImageService.ts b/packages/backend/src/core/activitypub/models/ApImageService.ts
index 79c5ae958a..0da312241f 100644
--- a/packages/backend/src/core/activitypub/models/ApImageService.ts
+++ b/packages/backend/src/core/activitypub/models/ApImageService.ts
@@ -10,9 +10,10 @@ import { DB_MAX_IMAGE_COMMENT_LENGTH } from '@/const.js';
 import { DriveService } from '@/core/DriveService.js';
 import type Logger from '@/logger.js';
 import { bindThis } from '@/decorators.js';
+import { checkHttps } from '@/misc/check-https.js';
 import { ApResolverService } from '../ApResolverService.js';
 import { ApLoggerService } from '../ApLoggerService.js';
-import { checkHttps } from '@/misc/check-https.js';
+import type { IObject } from '../type.js';
 
 @Injectable()
 export class ApImageService {
@@ -37,18 +38,22 @@ export class ApImageService {
 	 * Imageを作成します。
 	 */
 	@bindThis
-	public async createImage(actor: RemoteUser, value: any): Promise<DriveFile> {
+	public async createImage(actor: RemoteUser, value: string | IObject): Promise<DriveFile> {
 		// 投稿者が凍結されていたらスキップ
 		if (actor.isSuspended) {
 			throw new Error('actor has been suspended');
 		}
 
-		const image = await this.apResolverService.createResolver().resolve(value) as any;
+		const image = await this.apResolverService.createResolver().resolve(value);
 
 		if (image.url == null) {
 			throw new Error('invalid image: url not privided');
 		}
 
+		if (typeof image.url !== 'string') {
+			throw new Error('invalid image: unexpected type of url: ' + JSON.stringify(image.url, null, 2));
+		}
+
 		if (!checkHttps(image.url)) {
 			throw new Error('invalid image: unexpected schema of url: ' + image.url);
 		}
@@ -57,29 +62,19 @@ export class ApImageService {
 
 		const instance = await this.metaService.fetch();
 
-		let file = await this.driveService.uploadFromUrl({
+		const file = await this.driveService.uploadFromUrl({
 			url: image.url,
 			user: actor,
 			uri: image.url,
 			sensitive: image.sensitive,
 			isLink: !instance.cacheRemoteFiles,
-			comment: truncate(image.name, DB_MAX_IMAGE_COMMENT_LENGTH),
+			comment: truncate(image.name ?? undefined, DB_MAX_IMAGE_COMMENT_LENGTH),
 		});
+		if (!file.isLink || file.url === image.url) return file;
 
-		if (file.isLink) {
-			// URLが異なっている場合、同じ画像が以前に異なるURLで登録されていたということなので、
-			// URLを更新する
-			if (file.url !== image.url) {
-				await this.driveFilesRepository.update({ id: file.id }, {
-					url: image.url,
-					uri: image.url,
-				});
-
-				file = await this.driveFilesRepository.findOneByOrFail({ id: file.id });
-			}
-		}
-
-		return file;
+		// URLが異なっている場合、同じ画像が以前に異なるURLで登録されていたということなので、URLを更新する
+		await this.driveFilesRepository.update({ id: file.id }, { url: image.url, uri: image.url });
+		return await this.driveFilesRepository.findOneByOrFail({ id: file.id });
 	}
 
 	/**
@@ -89,7 +84,7 @@ export class ApImageService {
 	 * リモートサーバーからフェッチしてMisskeyに登録しそれを返します。
 	 */
 	@bindThis
-	public async resolveImage(actor: RemoteUser, value: any): Promise<DriveFile> {
+	public async resolveImage(actor: RemoteUser, value: string | IObject): Promise<DriveFile> {
 		// TODO
 
 		// リモートサーバーからフェッチしてきて登録
diff --git a/packages/backend/src/core/activitypub/models/ApMentionService.ts b/packages/backend/src/core/activitypub/models/ApMentionService.ts
index 9beefc8fcb..62ae3cf93d 100644
--- a/packages/backend/src/core/activitypub/models/ApMentionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApMentionService.ts
@@ -22,8 +22,8 @@ export class ApMentionService {
 	}
 
 	@bindThis
-	public async extractApMentions(tags: IObject | IObject[] | null | undefined, resolver: Resolver) {
-		const hrefs = unique(this.extractApMentionObjects(tags).map(x => x.href as string));
+	public async extractApMentions(tags: IObject | IObject[] | null | undefined, resolver: Resolver): Promise<User[]> {
+		const hrefs = unique(this.extractApMentionObjects(tags).map(x => x.href));
 
 		const limit = promiseLimit<User | null>(2);
 		const mentionedUsers = (await Promise.all(
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index 60a3e56800..35865a819d 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -20,7 +20,6 @@ import { UtilityService } from '@/core/UtilityService.js';
 import { bindThis } from '@/decorators.js';
 import { checkHttps } from '@/misc/check-https.js';
 import { getOneApId, getApId, getOneApHrefNullable, validPost, isEmoji, getApType } from '../type.js';
-// eslint-disable-next-line @typescript-eslint/consistent-type-imports
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApMfmService } from '../ApMfmService.js';
 import { ApDbResolverService } from '../ApDbResolverService.js';
@@ -72,13 +71,9 @@ export class ApNoteService {
 	}
 
 	@bindThis
-	public validateNote(object: IObject, uri: string) {
+	public validateNote(object: IObject, uri: string): Error | null {
 		const expectHost = this.utilityService.extractDbHost(uri);
 
-		if (object == null) {
-			return new Error('invalid Note: object is null');
-		}
-
 		if (!validPost.includes(getApType(object))) {
 			return new Error(`invalid Note: invalid object type ${getApType(object)}`);
 		}
@@ -110,6 +105,7 @@ export class ApNoteService {
 	 */
 	@bindThis
 	public async createNote(value: string | IObject, resolver?: Resolver, silent = false): Promise<Note | null> {
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 
 		const object = await resolver.resolve(value);
@@ -117,12 +113,10 @@ export class ApNoteService {
 		const entryUri = getApId(value);
 		const err = this.validateNote(object, entryUri);
 		if (err) {
-			this.logger.error(`${err.message}`, {
-				resolver: {
-					history: resolver.getHistory(),
-				},
-				value: value,
-				object: object,
+			this.logger.error(err.message, {
+				resolver: { history: resolver.getHistory() },
+				value,
+				object,
 			});
 			throw new Error('invalid note');
 		}
@@ -144,7 +138,11 @@ export class ApNoteService {
 		this.logger.info(`Creating the Note: ${note.id}`);
 
 		// 投稿者をフェッチ
-		const actor = await this.apPersonService.resolvePerson(getOneApId(note.attributedTo!), resolver) as RemoteUser;
+		if (note.attributedTo == null) {
+			throw new Error('invalid note.attributedTo: ' + note.attributedTo);
+		}
+
+		const actor = await this.apPersonService.resolvePerson(getOneApId(note.attributedTo), resolver) as RemoteUser;
 
 		// 投稿者が凍結されていたらスキップ
 		if (actor.isSuspended) {
@@ -164,59 +162,49 @@ export class ApNoteService {
 		}
 
 		const apMentions = await this.apMentionService.extractApMentions(note.tag, resolver);
-		const apHashtags = await extractApHashtags(note.tag);
+		const apHashtags = extractApHashtags(note.tag);
 
 		// 添付ファイル
 		// TODO: attachmentは必ずしもImageではない
 		// TODO: attachmentは必ずしも配列ではない
-		// Noteがsensitiveなら添付もsensitiveにする
-		const limit = promiseLimit(2);
-
-		note.attachment = Array.isArray(note.attachment) ? note.attachment : note.attachment ? [note.attachment] : [];
-		const files = note.attachment
-			.map(attach => attach.sensitive = note.sensitive)
-			? (await Promise.all(note.attachment.map(x => limit(() => this.apImageService.resolveImage(actor, x)) as Promise<DriveFile>)))
-				.filter(image => image != null)
-			: [];
+		const limit = promiseLimit<DriveFile>(2);
+		const files = (await Promise.all(toArray(note.attachment).map(attach => (
+			limit(() => this.apImageService.resolveImage(actor, {
+				...attach,
+				sensitive: note.sensitive, // Noteがsensitiveなら添付もsensitiveにする
+			}))
+		))));
 
 		// リプライ
 		const reply: Note | null = note.inReplyTo
-			? await this.resolveNote(note.inReplyTo, resolver).then(x => {
-				if (x == null) {
-					this.logger.warn('Specified inReplyTo, but not found');
-					throw new Error('inReplyTo not found');
-				} else {
+			? await this.resolveNote(note.inReplyTo, resolver)
+				.then(x => {
+					if (x == null) {
+						this.logger.warn('Specified inReplyTo, but not found');
+						throw new Error('inReplyTo not found');
+					}
+
 					return x;
-				}
-			}).catch(async err => {
-				this.logger.warn(`Error in inReplyTo ${note.inReplyTo} - ${err.statusCode ?? err}`);
-				throw err;
-			})
+				})
+				.catch(async err => {
+					this.logger.warn(`Error in inReplyTo ${note.inReplyTo} - ${err.statusCode ?? err}`);
+					throw err;
+				})
 			: null;
 
 		// 引用
-		let quote: Note | undefined | null;
+		let quote: Note | undefined | null = null;
 
 		if (note._misskey_quote || note.quoteUrl) {
-			const tryResolveNote = async (uri: string): Promise<{
-				status: 'ok';
-				res: Note | null;
-			} | {
-				status: 'permerror' | 'temperror';
-			}> => {
-				if (typeof uri !== 'string' || !uri.match(/^https?:/)) return { status: 'permerror' };
+			const tryResolveNote = async (uri: string): Promise<
+				| { status: 'ok'; res: Note }
+				| { status: 'permerror' | 'temperror' }
+			> => {
+				if (!uri.match(/^https?:/)) return { status: 'permerror' };
 				try {
 					const res = await this.resolveNote(uri);
-					if (res) {
-						return {
-							status: 'ok',
-							res,
-						};
-					} else {
-						return {
-							status: 'permerror',
-						};
-					}
+					if (res == null) return { status: 'permerror' };
+					return { status: 'ok', res };
 				} catch (e) {
 					return {
 						status: (e instanceof StatusError && e.isClientError) ? 'permerror' : 'temperror',
@@ -225,9 +213,9 @@ export class ApNoteService {
 			};
 
 			const uris = unique([note._misskey_quote, note.quoteUrl].filter((x): x is string => typeof x === 'string'));
-			const results = await Promise.all(uris.map(uri => tryResolveNote(uri)));
+			const results = await Promise.all(uris.map(tryResolveNote));
 
-			quote = results.filter((x): x is { status: 'ok', res: Note | null } => x.status === 'ok').map(x => x.res).find(x => x);
+			quote = results.filter((x): x is { status: 'ok', res: Note } => x.status === 'ok').map(x => x.res).at(0);
 			if (!quote) {
 				if (results.some(x => x.status === 'temperror')) {
 					throw new Error('quote resolve failed');
@@ -271,7 +259,7 @@ export class ApNoteService {
 
 		const emojis = await this.extractEmojis(note.tag ?? [], actor.host).catch(e => {
 			this.logger.info(`extractEmojis: ${e}`);
-			return [] as Emoji[];
+			return [];
 		});
 
 		const apEmojis = emojis.map(emoji => emoji.name);
@@ -309,19 +297,18 @@ export class ApNoteService {
 		const uri = typeof value === 'string' ? value : value.id;
 		if (uri == null) throw new Error('missing uri');
 
-		// ブロックしてたら中断
+		// ブロックしていたら中断
 		const meta = await this.metaService.fetch();
-		if (this.utilityService.isBlockedHost(meta.blockedHosts, this.utilityService.extractDbHost(uri))) throw new StatusError('blocked host', 451);
+		if (this.utilityService.isBlockedHost(meta.blockedHosts, this.utilityService.extractDbHost(uri))) {
+			throw new StatusError('blocked host', 451);
+		}
 
 		const unlock = await this.appLockService.getApLock(uri);
 
 		try {
 			//#region このサーバーに既に登録されていたらそれを返す
 			const exist = await this.fetchNote(uri);
-
-			if (exist) {
-				return exist;
-			}
+			if (exist) return exist;
 			//#endregion
 
 			if (uri.startsWith(this.config.url)) {
@@ -339,43 +326,41 @@ export class ApNoteService {
 
 	@bindThis
 	public async extractEmojis(tags: IObject | IObject[], host: string): Promise<Emoji[]> {
+		// eslint-disable-next-line no-param-reassign
 		host = this.utilityService.toPuny(host);
 
-		if (!tags) return [];
-
 		const eomjiTags = toArray(tags).filter(isEmoji);
 
 		const existingEmojis = await this.emojisRepository.findBy({
 			host,
-			name: In(eomjiTags.map(tag => tag.name!.replaceAll(':', ''))),
+			name: In(eomjiTags.map(tag => tag.name.replaceAll(':', ''))),
 		});
 
 		return await Promise.all(eomjiTags.map(async tag => {
-			const name = tag.name!.replaceAll(':', '');
+			const name = tag.name.replaceAll(':', '');
 			tag.icon = toSingle(tag.icon);
 
 			const exists = existingEmojis.find(x => x.name === name);
 
 			if (exists) {
-				if ((tag.updated != null && exists.updatedAt == null)
+				if ((exists.updatedAt == null)
 					|| (tag.id != null && exists.uri == null)
-					|| (tag.updated != null && exists.updatedAt != null && new Date(tag.updated) > exists.updatedAt)
-					|| (tag.icon!.url !== exists.originalUrl)
+					|| (new Date(tag.updated) > exists.updatedAt)
+					|| (tag.icon.url !== exists.originalUrl)
 				) {
 					await this.emojisRepository.update({
 						host,
 						name,
 					}, {
 						uri: tag.id,
-						originalUrl: tag.icon!.url,
-						publicUrl: tag.icon!.url,
+						originalUrl: tag.icon.url,
+						publicUrl: tag.icon.url,
 						updatedAt: new Date(),
 					});
 
-					return await this.emojisRepository.findOneBy({
-						host,
-						name,
-					}) as Emoji;
+					const emoji = await this.emojisRepository.findOneBy({ host, name });
+					if (emoji == null) throw new Error('emoji update failed');
+					return emoji;
 				}
 
 				return exists;
@@ -388,11 +373,11 @@ export class ApNoteService {
 				host,
 				name,
 				uri: tag.id,
-				originalUrl: tag.icon!.url,
-				publicUrl: tag.icon!.url,
+				originalUrl: tag.icon.url,
+				publicUrl: tag.icon.url,
 				updatedAt: new Date(),
 				aliases: [],
-			} as Partial<Emoji>).then(x => this.emojisRepository.findOneByOrFail(x.identifiers[0]));
+			}).then(x => this.emojisRepository.findOneByOrFail(x.identifiers[0]));
 		}));
 	}
 }
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index afe89e5a11..e8b65b3d42 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -3,7 +3,7 @@ import promiseLimit from 'promise-limit';
 import { DataSource } from 'typeorm';
 import { ModuleRef } from '@nestjs/core';
 import { DI } from '@/di-symbols.js';
-import type { BlockingsRepository, MutingsRepository, FollowingsRepository, InstancesRepository, UserProfilesRepository, UserPublickeysRepository, UsersRepository } from '@/models/index.js';
+import type { FollowingsRepository, InstancesRepository, UserProfilesRepository, UserPublickeysRepository, UsersRepository } from '@/models/index.js';
 import type { Config } from '@/config.js';
 import type { LocalUser, RemoteUser } from '@/models/entities/User.js';
 import { User } from '@/models/entities/User.js';
@@ -15,7 +15,6 @@ import type Logger from '@/logger.js';
 import type { Note } from '@/models/entities/Note.js';
 import type { IdService } from '@/core/IdService.js';
 import type { MfmService } from '@/core/MfmService.js';
-import type { Emoji } from '@/models/entities/Emoji.js';
 import { toArray } from '@/misc/prelude/array.js';
 import type { GlobalEventService } from '@/core/GlobalEventService.js';
 import type { FederatedInstanceService } from '@/core/FederatedInstanceService.js';
@@ -48,6 +47,8 @@ import type { IActor, IObject } from '../type.js';
 const nameLength = 128;
 const summaryLength = 2048;
 
+type Field = Record<'name' | 'value', string>;
+
 @Injectable()
 export class ApPersonService implements OnModuleInit {
 	private utilityService: UtilityService;
@@ -94,28 +95,10 @@ export class ApPersonService implements OnModuleInit {
 
 		@Inject(DI.followingsRepository)
 		private followingsRepository: FollowingsRepository,
-
-		//private utilityService: UtilityService,
-		//private userEntityService: UserEntityService,
-		//private idService: IdService,
-		//private globalEventService: GlobalEventService,
-		//private metaService: MetaService,
-		//private federatedInstanceService: FederatedInstanceService,
-		//private fetchInstanceMetadataService: FetchInstanceMetadataService,
-		//private cacheService: CacheService,
-		//private apResolverService: ApResolverService,
-		//private apNoteService: ApNoteService,
-		//private apImageService: ApImageService,
-		//private apMfmService: ApMfmService,
-		//private mfmService: MfmService,
-		//private hashtagService: HashtagService,
-		//private usersChart: UsersChart,
-		//private instanceChart: InstanceChart,
-		//private apLoggerService: ApLoggerService,
 	) {
 	}
 
-	onModuleInit() {
+	onModuleInit(): void {
 		this.utilityService = this.moduleRef.get('UtilityService');
 		this.userEntityService = this.moduleRef.get('UserEntityService');
 		this.driveFileEntityService = this.moduleRef.get('DriveFileEntityService');
@@ -153,10 +136,6 @@ export class ApPersonService implements OnModuleInit {
 	private validateActor(x: IObject, uri: string): IActor {
 		const expectHost = this.punyHost(uri);
 
-		if (x == null) {
-			throw new Error('invalid Actor: object is null');
-		}
-
 		if (!isActor(x)) {
 			throw new Error(`invalid Actor type '${x.type}'`);
 		}
@@ -218,21 +197,19 @@ export class ApPersonService implements OnModuleInit {
 	 */
 	@bindThis
 	public async fetchPerson(uri: string): Promise<LocalUser | RemoteUser | null> {
-		if (typeof uri !== 'string') throw new Error('uri is not string');
-
-		const cached = this.cacheService.uriPersonCache.get(uri) as LocalUser | RemoteUser | null;
+		const cached = this.cacheService.uriPersonCache.get(uri) as LocalUser | RemoteUser | null | undefined;
 		if (cached) return cached;
 
 		// URIがこのサーバーを指しているならデータベースからフェッチ
 		if (uri.startsWith(`${this.config.url}/`)) {
 			const id = uri.split('/').pop();
-			const u = await this.usersRepository.findOneBy({ id }) as LocalUser;
+			const u = await this.usersRepository.findOneBy({ id }) as LocalUser | null;
 			if (u) this.cacheService.uriPersonCache.set(uri, u);
 			return u;
 		}
 
 		//#region このサーバーに既に登録されていたらそれを返す
-		const exist = await this.usersRepository.findOneBy({ uri }) as LocalUser | RemoteUser;
+		const exist = await this.usersRepository.findOneBy({ uri }) as LocalUser | RemoteUser | null;
 
 		if (exist) {
 			this.cacheService.uriPersonCache.set(uri, exist);
@@ -254,9 +231,11 @@ export class ApPersonService implements OnModuleInit {
 			throw new StatusError('cannot resolve local user', 400, 'cannot resolve local user');
 		}
 
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 
-		const object = await resolver.resolve(uri) as any;
+		const object = await resolver.resolve(uri);
+		if (object.id == null) throw new Error('invalid object.id: ' + object.id);
 
 		const person = this.validateActor(object, uri);
 
@@ -264,9 +243,9 @@ export class ApPersonService implements OnModuleInit {
 
 		const host = this.punyHost(object.id);
 
-		const { fields } = this.analyzeAttachments(person.attachment ?? []);
+		const fields = this.analyzeAttachments(person.attachment ?? []);
 
-		const tags = extractApHashtags(person.tag).map(tag => normalizeForSearch(tag)).splice(0, 32);
+		const tags = extractApHashtags(person.tag).map(normalizeForSearch).splice(0, 32);
 
 		const isBot = getApType(object) === 'Service';
 
@@ -279,7 +258,7 @@ export class ApPersonService implements OnModuleInit {
 		}
 
 		// Create user
-		let user: RemoteUser;
+		let user: RemoteUser | null = null;
 		try {
 		// Start transaction
 			await this.db.transaction(async transactionalEntityManager => {
@@ -290,16 +269,16 @@ export class ApPersonService implements OnModuleInit {
 					createdAt: new Date(),
 					lastFetchedAt: new Date(),
 					name: truncate(person.name, nameLength),
-					isLocked: !!person.manuallyApprovesFollowers,
+					isLocked: person.manuallyApprovesFollowers,
 					movedToUri: person.movedTo,
 					movedAt: person.movedTo ? new Date() : null,
 					alsoKnownAs: person.alsoKnownAs,
-					isExplorable: !!person.discoverable,
+					isExplorable: person.discoverable,
 					username: person.preferredUsername,
-					usernameLower: person.preferredUsername!.toLowerCase(),
+					usernameLower: person.preferredUsername?.toLowerCase(),
 					host,
 					inbox: person.inbox,
-					sharedInbox: person.sharedInbox ?? (person.endpoints ? person.endpoints.sharedInbox : undefined),
+					sharedInbox: person.sharedInbox ?? person.endpoints?.sharedInbox,
 					followersUri: person.followers ? getApId(person.followers) : undefined,
 					featured: person.featured ? getApId(person.featured) : undefined,
 					uri: person.id,
@@ -311,9 +290,9 @@ export class ApPersonService implements OnModuleInit {
 				await transactionalEntityManager.save(new UserProfile({
 					userId: user.id,
 					description: person.summary ? this.apMfmService.htmlToMfm(truncate(person.summary, summaryLength), person.tag) : null,
-					url: url,
+					url,
 					fields,
-					birthday: bday ? bday[0] : null,
+					birthday: bday?.[0] ?? null,
 					location: person['vcard:Address'] ?? null,
 					userHost: host,
 				}));
@@ -330,21 +309,18 @@ export class ApPersonService implements OnModuleInit {
 		// duplicate key error
 			if (isDuplicateKeyValueError(e)) {
 			// /users/@a => /users/:id のように入力がaliasなときにエラーになることがあるのを対応
-				const u = await this.usersRepository.findOneBy({
-					uri: person.id,
-				});
+				const u = await this.usersRepository.findOneBy({ uri: person.id });
+				if (u == null) throw new Error('already registered');
 
-				if (u) {
-					user = u as RemoteUser;
-				} else {
-					throw new Error('already registered');
-				}
+				user = u as RemoteUser;
 			} else {
 				this.logger.error(e instanceof Error ? e : new Error(e as string));
 				throw e;
 			}
 		}
 
+		if (user == null) throw new Error('failed to create user: user is null');
+
 		// Register host
 		this.federatedInstanceService.fetch(host).then(async i => {
 			this.instancesRepository.increment({ id: i.id }, 'usersCount', 1);
@@ -354,29 +330,26 @@ export class ApPersonService implements OnModuleInit {
 			}
 		});
 
-		this.usersChart.update(user!, true);
+		this.usersChart.update(user, true);
 
 		// ハッシュタグ更新
-		this.hashtagService.updateUsertags(user!, tags);
+		this.hashtagService.updateUsertags(user, tags);
 
 		//#region アバターとヘッダー画像をフェッチ
-		const [avatar, banner] = await Promise.all([
-			person.icon,
-			person.image,
-		].map(img =>
-			img == null
-				? Promise.resolve(null)
-				: this.apImageService.resolveImage(user!, img).catch(() => null),
-		));
+		const [avatar, banner] = await Promise.all([person.icon, person.image].map(img => {
+			if (img == null) return null;
+			if (user == null) throw new Error('failed to create user: user is null');
+			return this.apImageService.resolveImage(user, img).catch(() => null);
+		}));
 
-		const avatarId = avatar ? avatar.id : null;
-		const bannerId = banner ? banner.id : null;
+		const avatarId = avatar?.id ?? null;
+		const bannerId = banner?.id ?? null;
 		const avatarUrl = avatar ? this.driveFileEntityService.getPublicUrl(avatar, 'avatar') : null;
 		const bannerUrl = banner ? this.driveFileEntityService.getPublicUrl(banner) : null;
-		const avatarBlurhash = avatar ? avatar.blurhash : null;
-		const bannerBlurhash = banner ? banner.blurhash : null;
+		const avatarBlurhash = avatar?.blurhash ?? null;
+		const bannerBlurhash = banner?.blurhash ?? null;
 
-		await this.usersRepository.update(user!.id, {
+		await this.usersRepository.update(user.id, {
 			avatarId,
 			bannerId,
 			avatarUrl,
@@ -385,30 +358,28 @@ export class ApPersonService implements OnModuleInit {
 			bannerBlurhash,
 		});
 
-		user!.avatarId = avatarId;
-		user!.bannerId = bannerId;
-		user!.avatarUrl = avatarUrl;
-		user!.bannerUrl = bannerUrl;
-		user!.avatarBlurhash = avatarBlurhash;
-		user!.bannerBlurhash = bannerBlurhash;
+		user.avatarId = avatarId;
+		user.bannerId = bannerId;
+		user.avatarUrl = avatarUrl;
+		user.bannerUrl = bannerUrl;
+		user.avatarBlurhash = avatarBlurhash;
+		user.bannerBlurhash = bannerBlurhash;
 		//#endregion
 
 		//#region カスタム絵文字取得
 		const emojis = await this.apNoteService.extractEmojis(person.tag ?? [], host).catch(err => {
 			this.logger.info(`extractEmojis: ${err}`);
-			return [] as Emoji[];
+			return [];
 		});
 
 		const emojiNames = emojis.map(emoji => emoji.name);
 
-		await this.usersRepository.update(user!.id, {
-			emojis: emojiNames,
-		});
+		await this.usersRepository.update(user.id, { emojis: emojiNames });
 		//#endregion
 
-		await this.updateFeatured(user!.id, resolver).catch(err => this.logger.error(err));
+		await this.updateFeatured(user.id, resolver).catch(err => this.logger.error(err));
 
-		return user!;
+		return user;
 	}
 
 	/**
@@ -426,18 +397,14 @@ export class ApPersonService implements OnModuleInit {
 		if (typeof uri !== 'string') throw new Error('uri is not string');
 
 		// URIがこのサーバーを指しているならスキップ
-		if (uri.startsWith(`${this.config.url}/`)) {
-			return;
-		}
+		if (uri.startsWith(`${this.config.url}/`)) return;
 
 		//#region このサーバーに既に登録されているか
 		const exist = await this.usersRepository.findOneBy({ uri }) as RemoteUser | null;
-
-		if (exist === null) {
-			return;
-		}
+		if (exist === null) return;
 		//#endregion
 
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 
 		const object = hint ?? await resolver.resolve(uri);
@@ -447,26 +414,22 @@ export class ApPersonService implements OnModuleInit {
 		this.logger.info(`Updating the Person: ${person.id}`);
 
 		// アバターとヘッダー画像をフェッチ
-		const [avatar, banner] = await Promise.all([
-			person.icon,
-			person.image,
-		].map(img =>
-			img == null
-				? Promise.resolve(null)
-				: this.apImageService.resolveImage(exist, img).catch(() => null),
-		));
+		const [avatar, banner] = await Promise.all([person.icon, person.image].map(img => {
+			if (img == null) return null;
+			return this.apImageService.resolveImage(exist, img).catch(() => null);
+		}));
 
 		// カスタム絵文字取得
 		const emojis = await this.apNoteService.extractEmojis(person.tag ?? [], exist.host).catch(e => {
 			this.logger.info(`extractEmojis: ${e}`);
-			return [] as Emoji[];
+			return [];
 		});
 
 		const emojiNames = emojis.map(emoji => emoji.name);
 
-		const { fields } = this.analyzeAttachments(person.attachment ?? []);
+		const fields = this.analyzeAttachments(person.attachment ?? []);
 
-		const tags = extractApHashtags(person.tag).map(tag => normalizeForSearch(tag)).splice(0, 32);
+		const tags = extractApHashtags(person.tag).map(normalizeForSearch).splice(0, 32);
 
 		const bday = person['vcard:bday']?.match(/^\d{4}-\d{2}-\d{2}/);
 
@@ -479,7 +442,7 @@ export class ApPersonService implements OnModuleInit {
 		const updates = {
 			lastFetchedAt: new Date(),
 			inbox: person.inbox,
-			sharedInbox: person.sharedInbox ?? (person.endpoints ? person.endpoints.sharedInbox : undefined),
+			sharedInbox: person.sharedInbox ?? person.endpoints?.sharedInbox,
 			followersUri: person.followers ? getApId(person.followers) : undefined,
 			featured: person.featured,
 			emojis: emojiNames,
@@ -487,18 +450,29 @@ export class ApPersonService implements OnModuleInit {
 			tags,
 			isBot: getApType(object) === 'Service',
 			isCat: (person as any).isCat === true,
-			isLocked: !!person.manuallyApprovesFollowers,
+			isLocked: person.manuallyApprovesFollowers,
 			movedToUri: person.movedTo ?? null,
 			alsoKnownAs: person.alsoKnownAs ?? null,
-			isExplorable: !!person.discoverable,
+			isExplorable: person.discoverable,
 		} as Partial<RemoteUser> & Pick<RemoteUser, 'isBot' | 'isCat' | 'isLocked' | 'movedToUri' | 'alsoKnownAs' | 'isExplorable'>;
 
-		const moving =
+		const moving = ((): boolean => {
 			// 移行先がない→ある
-			(!exist.movedToUri && updates.movedToUri) ||
+			if (
+				exist.movedToUri === null &&
+				updates.movedToUri
+			) return true;
+
 			// 移行先がある→別のもの
-			(exist.movedToUri !== updates.movedToUri && exist.movedToUri && updates.movedToUri);
+			if (
+				exist.movedToUri !== null &&
+				updates.movedToUri !== null &&
+				exist.movedToUri !== updates.movedToUri
+			) return true;
+
 			// 移行先がある→ない、ない→ないは無視
+			return false;
+		})();
 
 		if (moving) updates.movedAt = new Date();
 
@@ -525,10 +499,10 @@ export class ApPersonService implements OnModuleInit {
 		}
 
 		await this.userProfilesRepository.update({ userId: exist.id }, {
-			url: url,
+			url,
 			fields,
 			description: person.summary ? this.apMfmService.htmlToMfm(truncate(person.summary, summaryLength), person.tag) : null,
-			birthday: bday ? bday[0] : null,
+			birthday: bday?.[0] ?? null,
 			location: person['vcard:Address'] ?? null,
 		});
 
@@ -538,11 +512,10 @@ export class ApPersonService implements OnModuleInit {
 		this.hashtagService.updateUsertags(exist, tags);
 
 		// 該当ユーザーが既にフォロワーになっていた場合はFollowingもアップデートする
-		await this.followingsRepository.update({
-			followerId: exist.id,
-		}, {
-			followerSharedInbox: person.sharedInbox ?? (person.endpoints ? person.endpoints.sharedInbox : undefined),
-		});
+		await this.followingsRepository.update(
+			{ followerId: exist.id },
+			{ followerSharedInbox: person.sharedInbox ?? person.endpoints?.sharedInbox },
+		);
 
 		await this.updateFeatured(exist.id, resolver).catch(err => this.logger.error(err));
 
@@ -580,27 +553,22 @@ export class ApPersonService implements OnModuleInit {
 	 */
 	@bindThis
 	public async resolvePerson(uri: string, resolver?: Resolver): Promise<LocalUser | RemoteUser> {
-		if (typeof uri !== 'string') throw new Error('uri is not string');
-
 		//#region このサーバーに既に登録されていたらそれを返す
 		const exist = await this.fetchPerson(uri);
-
-		if (exist) {
-			return exist;
-		}
+		if (exist) return exist;
 		//#endregion
 
 		// リモートサーバーからフェッチしてきて登録
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 		return await this.createPerson(uri, resolver);
 	}
 
 	@bindThis
-	public analyzeAttachments(attachments: IObject | IObject[] | undefined) {
-		const fields: {
-		name: string,
-		value: string
-	}[] = [];
+	// TODO: `attachments`が`IObject`だった場合、返り値が`[]`になるようだが構わないのか？
+	public analyzeAttachments(attachments: IObject | IObject[] | undefined): Field[] {
+		const fields: Field[] = [];
+
 		if (Array.isArray(attachments)) {
 			for (const attachment of attachments.filter(isPropertyValue)) {
 				fields.push({
@@ -610,11 +578,11 @@ export class ApPersonService implements OnModuleInit {
 			}
 		}
 
-		return { fields };
+		return fields;
 	}
 
 	@bindThis
-	public async updateFeatured(userId: User['id'], resolver?: Resolver) {
+	public async updateFeatured(userId: User['id'], resolver?: Resolver): Promise<void> {
 		const user = await this.usersRepository.findOneByOrFail({ id: userId });
 		if (!this.userEntityService.isRemoteUser(user)) return;
 		if (!user.featured) return;
@@ -643,13 +611,13 @@ 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(note => note != null)) {
+			for (const note of featuredNotes.filter((note): note is Note => note != null)) {
 				td -= 1000;
 				transactionalEntityManager.insert(UserNotePining, {
 					id: this.idService.genId(new Date(Date.now() + td)),
 					createdAt: new Date(),
 					userId: user.id,
-					noteId: note!.id,
+					noteId: note.id,
 				});
 			}
 		});
diff --git a/packages/backend/src/core/activitypub/models/ApQuestionService.ts b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
index 13a2f0fa5c..229a44f90f 100644
--- a/packages/backend/src/core/activitypub/models/ApQuestionService.ts
+++ b/packages/backend/src/core/activitypub/models/ApQuestionService.ts
@@ -4,12 +4,12 @@ import type { NotesRepository, PollsRepository } from '@/models/index.js';
 import type { Config } from '@/config.js';
 import type { IPoll } from '@/models/entities/Poll.js';
 import type Logger from '@/logger.js';
+import { bindThis } from '@/decorators.js';
 import { isQuestion } from '../type.js';
 import { ApLoggerService } from '../ApLoggerService.js';
 import { ApResolverService } from '../ApResolverService.js';
 import type { Resolver } from '../ApResolverService.js';
 import type { IObject, IQuestion } from '../type.js';
-import { bindThis } from '@/decorators.js';
 
 @Injectable()
 export class ApQuestionService {
@@ -33,33 +33,25 @@ export class ApQuestionService {
 
 	@bindThis
 	public async extractPollFromQuestion(source: string | IObject, resolver?: Resolver): Promise<IPoll> {
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 
 		const question = await resolver.resolve(source);
+		if (!isQuestion(question)) throw new Error('invalid type');
 
-		if (!isQuestion(question)) {
-			throw new Error('invalid type');
-		}
+		const multiple = question.oneOf === undefined;
+		if (multiple && question.anyOf === undefined) throw new Error('invalid question');
 
-		const multiple = !question.oneOf;
 		const expiresAt = question.endTime ? new Date(question.endTime) : question.closed ? new Date(question.closed) : null;
 
-		if (multiple && !question.anyOf) {
-			throw new Error('invalid question');
-		}
+		const choices = question[multiple ? 'anyOf' : 'oneOf']
+			?.map((x) => x.name)
+			.filter((x): x is string => typeof x === 'string')
+			?? [];
 
-		const choices = question[multiple ? 'anyOf' : 'oneOf']!
-			.map((x, i) => x.name!);
+		const votes = question[multiple ? 'anyOf' : 'oneOf']?.map((x) => x.replies?.totalItems ?? x._misskey_votes ?? 0);
 
-		const votes = question[multiple ? 'anyOf' : 'oneOf']!
-			.map((x, i) => x.replies && x.replies.totalItems || x._misskey_votes || 0);
-
-		return {
-			choices,
-			votes,
-			multiple,
-			expiresAt,
-		};
+		return { choices, votes, multiple, expiresAt };
 	}
 
 	/**
@@ -68,8 +60,9 @@ export class ApQuestionService {
 	 * @returns true if updated
 	 */
 	@bindThis
-	public async updateQuestion(value: any, resolver?: Resolver) {
+	public async updateQuestion(value: string | IObject, resolver?: Resolver): Promise<boolean> {
 		const uri = typeof value === 'string' ? value : value.id;
+		if (uri == null) throw new Error('uri is null');
 
 		// URIがこのサーバーを指しているならスキップ
 		if (uri.startsWith(this.config.url + '/')) throw new Error('uri points local');
@@ -83,6 +76,7 @@ export class ApQuestionService {
 		//#endregion
 
 		// resolve new Question object
+		// eslint-disable-next-line no-param-reassign
 		if (resolver == null) resolver = this.apResolverService.createResolver();
 		const question = await resolver.resolve(value) as IQuestion;
 		this.logger.debug(`fetched question: ${JSON.stringify(question, null, 2)}`);
@@ -90,12 +84,14 @@ export class ApQuestionService {
 		if (question.type !== 'Question') throw new Error('object is not a Question');
 
 		const apChoices = question.oneOf ?? question.anyOf;
+		if (apChoices == null) throw new Error('invalid apChoices: ' + apChoices);
 
 		let changed = false;
 
 		for (const choice of poll.choices) {
 			const oldCount = poll.votes[poll.choices.indexOf(choice)];
-			const newCount = apChoices!.filter(ap => ap.name === choice)[0].replies!.totalItems;
+			const newCount = apChoices.filter(ap => ap.name === choice).at(0)?.replies?.totalItems;
+			if (newCount == null) throw new Error('invalid newCount: ' + newCount);
 
 			if (oldCount !== newCount) {
 				changed = true;
@@ -103,9 +99,7 @@ export class ApQuestionService {
 			}
 		}
 
-		await this.pollsRepository.update({ noteId: note.id }, {
-			votes: poll.votes,
-		});
+		await this.pollsRepository.update({ noteId: note.id }, { votes: poll.votes });
 
 		return changed;
 	}
diff --git a/packages/backend/src/core/activitypub/models/tag.ts b/packages/backend/src/core/activitypub/models/tag.ts
index 803846a0b0..9aeb843562 100644
--- a/packages/backend/src/core/activitypub/models/tag.ts
+++ b/packages/backend/src/core/activitypub/models/tag.ts
@@ -2,7 +2,7 @@ import { toArray } from '@/misc/prelude/array.js';
 import { isHashtag } from '../type.js';
 import type { IObject, IApHashtag } from '../type.js';
 
-export function extractApHashtags(tags: IObject | IObject[] | null | undefined) {
+export function extractApHashtags(tags: IObject | IObject[] | null | undefined): string[] {
 	if (tags == null) return [];
 
 	const hashtags = extractApHashtagObjects(tags);
diff --git a/packages/backend/src/misc/check-https.ts b/packages/backend/src/misc/check-https.ts
index b33f019973..612032fe97 100644
--- a/packages/backend/src/misc/check-https.ts
+++ b/packages/backend/src/misc/check-https.ts
@@ -1,4 +1,4 @@
-export function checkHttps(url: string) {
-    return url.startsWith('https://') ||
-        (url.startsWith('http://') && process.env.NODE_ENV !== 'production');
+export function checkHttps(url: string): boolean {
+	return url.startsWith('https://') ||
+		(url.startsWith('http://') && process.env.NODE_ENV !== 'production');
 }