undefined is not iterable (cannot read property Symbol(Symbol.iterator))

I'm trying to loop through a fileList in order to perform a delete query. First i fetched data from table "files" in database where attribute "postnumber"=user input. Then it is saved into the "fileList:Files[]". Then a loop through this fileList in order to perform a delete query. but it keeps saying that

"ERROR TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))". See this image =>
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forum-admin-list.component.ts

import { FileService } from 'src/app/shared/file.service';
import { Files } from 'src/app/shared/files.model';
export class ForumAdminListComponent {
fileList:Files[];
onDelete(pNo:string){
this.fservice.getPost(pNo).subscribe(actionArray => {
this.fileList = actionArray.map(item => {
return {
id: item.payload.doc.id,
...item.payload.doc.data()
} as Files;
})
});
for(let i of this.fileList){
this.storage.storage.refFromURL(i.path).delete();
this.firestore.doc("files/"+i.id).delete();
}
}
}


files.model.ts

export class Files {
id:string;
pNo:string;
downloadURL:string;
path:string;
}


file.service.ts

export class FileService {
formData: Files;
constructor(private firestore: AngularFirestore) { }

getPost(userRef){
return this.firestore.collection('files',ref=>ref.where('pNo','==',userRef)).snapshotChanges();
}
}

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