Unexpected value 'undefined' declared by the module 'AppModule'
Solution 1:
I got the same error , sometimes this issue occur and you only need to re-run the server using ng serve or whatever CLI you use , as mentioned here
Solution 2:
I faced the same error and I discovered the reason.
The reason was two commas ,, in any array (for example: imports property) like this.
@NgModule({
imports: [
CommonModule, FormsModule,,
]})