refactor: 可読性のため一部でArray.prototype.atを使うように (#11274)

* refactor: `Array.prototype.at`を使うように

* fixup! refactor: `Array.prototype.at`を使うように

packages/backend/src/queue/processors/ExportMutingProcessorService.ts

@@ -3,7 +3,7 @@ import { Inject, Injectable } from '@nestjs/common';
 import { IsNull, MoreThan } from 'typeorm';
 import { format as dateFormat } from 'date-fns';
 import { DI } from '@/di-symbols.js';
-import type { MutingsRepository, UsersRepository, BlockingsRepository } from '@/models/index.js';
+import type { MutingsRepository, UsersRepository, BlockingsRepository, Muting } from '@/models/index.js';
 import type { Config } from '@/config.js';
 import type Logger from '@/logger.js';
 import { DriveService } from '@/core/DriveService.js';
@@ -56,7 +56,7 @@ export class ExportMutingProcessorService {
 			const stream = fs.createWriteStream(path, { flags: 'a' });
 
 			let exportedCount = 0;
-			let cursor: any = null;
+			let cursor: Muting['id'] | null = null;
 
 			while (true) {
 				const mutes = await this.mutingsRepository.find({
@@ -76,7 +76,7 @@ export class ExportMutingProcessorService {
 					break;
 				}
 
-				cursor = mutes[mutes.length - 1].id;
+				cursor = mutes.at(-1)?.id ?? null;
 
 				for (const mute of mutes) {
 					const u = await this.usersRepository.findOneBy({ id: mute.muteeId });