Afte upgrading to Angular 9 (from Angular 8) and running `ng build` I am getting 

```none
ERROR in Failed to list lazy routes: Unknown module './src/app/app.module#AppModule'.

```

It seems that the main app module cannot be found. 

This is my **main.ts** file:

```js
import { enableProdMode } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';

import { AppModule } from './app/app.module';
import { environment } from './environments/environment';

if (environment.production) {
  enableProdMode();
}

platformBrowserDynamic().bootstrapModule(AppModule)
  .catch(err => console.error(err));

```

I have created a new project and was able to run it successfully.

This means that there changed something from 8 to 9.

Any ideas what I have to change?