生产环境启动Nest实例时出现导入数组异常错误

使用NODE_ENV=production nest build构建NestJS应用后，在MacBook本地及Vagrant模拟的生产环境中，通过NODE_ENV=production nest start可正常启动，但在运行同版本Node.js 16.20的生产机器上启动时报错：

[Nest] 1108076 - 06/12/2023, 9:54:51 PM LOG [NestFactory] Starting Nest application...
[Nest] 1108076 - 06/12/2023, 9:54:51 PM ERROR [ExceptionHandler] Nest cannot create the AppModule instance.
Received an unexpected value at index [3] of the AppModule "imports" array.

Scope []
Error: Nest cannot create the AppModule instance.
Received an unexpected value at index [3] of the AppModule "imports" array.

Scope []
at DependenciesScanner.scanForModules (/home/check-inventory/test/node_modules/@nestjs/core/scanner.js:56:23)
at processTicksAndRejections (node:internal/process/task_queues:96:5)
at async DependenciesScanner.scan (/home/check-inventory/test/node_modules/@nestjs/core/scanner.js:27:9)
at async /home/check-inventory/test/node_modules/@nestjs/core/nest-factory.js:107:17
at async Function.asyncRun (/home/check-inventory/test/node_modules/@nestjs/core/errors/exceptions-zone.js:22:13)
at async NestFactoryStatic.initialize (/home/check-inventory/test/node_modules/@nestjs/core/nest-factory.js:106:13)
at async NestFactoryStatic.create (/home/check-inventory/test/node_modules/@nestjs/core/nest-factory.js:42:9)
at async bootstrap (/home/check-inventory/test/dist/src/main.js:13:17)

已通过scp传输本地构建的dist和node_modules至生产机器并调整权限，但问题仍未解决。

AppModule代码如下：

import { MiddlewareConsumer, Module, NestModule } from "@nestjs/common";
import { AppController } from "./app.controller";
import { AppService } from "./app.service";
import { TypeOrmModule } from "@nestjs/typeorm";
import { ConfigModule } from "@nestjs/config";
import { UsersModule } from "./users/users.module";
import { GroupsModule } from "./groups/groups.module";
import { RequestsModule } from "./requests/requests.module";
import { CategoriesModule } from "./categories/categories.module";
import { ItemsModule } from "./items/items.module";
import { UserInjectMiddleware } from "./middleware/user-inject.middleware";
import { TrackerModule } from "./tracker/tracker.module";
import { ScheduleModule } from "@nestjs/schedule";
import { SerialsModule } from "./serials/serials.module";
import { SocketModule } from "./socket/socket.module";
import { StoragesModule } from "./storages/storages.module";
import { AuthModule } from "./auth/auth.module";
import { APP_GUARD } from "@nestjs/core";
import { AzureValidatorGuard } from "./auth/azure-validator.guard";
import { RolesGuard } from "./auth/roles.guard";
import { StatisticsModule } from "./statistics/statistics.module";
import { config } from "./dataSource.config";

const env = process.env.NODE_ENV || "production";

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      envFilePath: `../.env.${env}`,
    }),
    TypeOrmModule.forRoot(config),
    ScheduleModule.forRoot(),
    process.env.EASYPOST_APIKEY ? TrackerModule : null,
    UsersModule,
    GroupsModule,
    RequestsModule,
    CategoriesModule,
    ItemsModule,
    SerialsModule,
    StoragesModule,
    SocketModule,
    AuthModule,
    StatisticsModule,
  ],
  controllers: [AppController],
  providers: [
    AppService,
    {
      provide: APP_GUARD,
      useClass: AzureValidatorGuard,
    },
    {
      provide: APP_GUARD,
      useClass: RolesGuard,
    },
  ],
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(UserInjectMiddleware).forRoutes("*");
  }
}

问题出在AppModule的imports数组里的这一行：

process.env.EASYPOST_APIKEY ? TrackerModule : null,

当生产机器上未配置EASYPOST_APIKEY环境变量时，null会被注入到imports数组的第3位（索引从0开始），而NestJS的模块imports数组不允许存在null或undefined这类无效值，这就是启动报错的核心原因。本地环境能正常启动，大概率是因为本地已经配置了该环境变量，不会触发null的情况。

提供两种可行的解决方法：

• 方案一：过滤无效值
  将imports数组改为动态生成的形式，自动过滤掉所有假值（null、undefined等）：

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      envFilePath: `../.env.${env}`,
    }),
    TypeOrmModule.forRoot(config),
    ScheduleModule.forRoot(),
    ...(process.env.EASYPOST_APIKEY ? [TrackerModule] : []),
    UsersModule,
    GroupsModule,
    RequestsModule,
    CategoriesModule,
    ItemsModule,
    SerialsModule,
    StoragesModule,
    SocketModule,
    AuthModule,
    StatisticsModule,
  ].filter(Boolean),
  // 其余配置保持不变
})

这里用扩展运算符...将条件模块转为数组，再通过filter(Boolean)过滤掉所有无效值。

• 方案二：提前构建imports数组
  先在模块外构建好完整的imports数组，再传入@Module装饰器：

const imports = [
  ConfigModule.forRoot({
    isGlobal: true,
    envFilePath: `../.env.${env}`,
  }),
  TypeOrmModule.forRoot(config),
  ScheduleModule.forRoot(),
  UsersModule,
  GroupsModule,
  RequestsModule,
  CategoriesModule,
  ItemsModule,
  SerialsModule,
  StoragesModule,
  SocketModule,
  AuthModule,
  StatisticsModule,
];

if (process.env.EASYPOST_APIKEY) {
  imports.splice(3, 0, TrackerModule); // 将模块插入到原位置
}

@Module({
  imports,
  // 其余配置保持不变
})

内容的提问来源于stack exchange，提问作者Daniel Terletzkiy