Angular Material, Autocomplete loading indicator and showing text (no results found)

Feature Description

I need to show loading when searching for data and also show text when no record is found. I have the following html excerpt:

<input
    matInput
    [matAutocomplete]="auto"
    [formControl]="formControl"
    [formlyAttributes]="field"
    [placeholder]="to.placeholder"
    [errorStateMatcher]="errorStateMatcher"
/>

<mat-icon class="arrow-autocomplete">arrow_drop_down</mat-icon>

<mat-autocomplete
    #auto="matAutocomplete"
    [displayWith]="displayFn.bind(this)">

    <mat-option *ngIf="isLoading" class="is-loading">
        <mat-spinner diameter="25"></mat-spinner>
    </mat-option>

    <ng-container *ngIf="!isLoading">
        <mat-option *ngFor="let value of result$ | async" [value]="value">
            <ng-container *ngFor="let ky of to.filterKeys; let index = index">
                {{
                index !== to.filterKeys.length - 1
                    ? value[ky] + ' - '
                    : value[ky]
                }}
            </ng-container>
            <ng-container *ngIf="!to.filterKeys">
                {{ value }}
            </ng-container>
        </mat-option>
    </ng-container>

</mat-autocomplete>

Component.ts code:

ngOnInit(): void {
        super.ngOnInit();

        this._unsubscribeAll = new Subject();
        this.isLoading = false;

        this.result$ = this.formControl.valueChanges.pipe(
            takeUntil(this._unsubscribeAll),
            debounceTime(300),
            startWith(''),
            tap(() => {
                this.isLoading = true
            }),
            switchMap(term => this.to.filter(term))
        );
    }

for loading, I would control it with the tap() method, but my problem is how to know that the request inside switchMap(term => this.to.filter(term)) was finished, so I set the loading variable to false?

my second problem is how to show a registration message not found, when the server returns an empty array, because I am working with async.