I tend to combine *ngIf and async like so:

My component will have an Observable (or in your case a Promise), with a variable name that ends with $. This naming pattern comes from the observable naming guide here

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
})
export class AppComponent {
  //Create a subject with an initial value
  //Keep the subject private so only this component may emit value
  private _mySubject = new BehaviorSubject<any>('initial value!');

  //Expose the observable as a public variable
  //This allows the template to listen for values
  get myObservable$() {
    return this._mySubject.asObservable();
  }

  //helpers for demo!

  emitNull() {
    this._mySubject.next(null);
  }

  emitUndefined() {
    this._mySubject.next(undefined);
  }

  emitNumber(number) {
    this._mySubject.next(number);
  }

  emitText(text) {
    console.log(text);
    this._mySubject.next(text);
  }
}

Then my template:

<div>
  <button (click)="emitNull()">Emit Null</button>
</div>
<div>
  <button (click)="emitUndefined()">Emit Undefined</button>
</div>
<div>
  <button (click)="emitNumber(num.value)">Emit Number</button>
  <input type="number" #num value="42" />
</div>
<div>
  <button (click)="emitText(txt.value)">Emit String</button>
  <input type="text" #txt value="foo" />
</div>

<br />

<h1>Value:</h1>
<ng-container *ngIf="myObservable$ | async as value; else other">
  <div>{{ value }}</div>
  ​ ​</ng-container
>

<ng-template #other>
  <div>The value was null, undefined or empty string</div>
</ng-template>

The template essentially reads as:

if(somevalue) 
    render a div displaying the value
else 
    render a div with text "The value was null..."

The key thing is that async is a pipe. A pipe always transforms some input. In this case, we're passing in an observable (or a promise) and getting some output.

So putting it all together, the template is:

1. Subscribing to the observable (or then'ing in the case of a promise),
2. Outputting a something whenever a new value is emitted, capturing it in a variable named value
3. Performing the if check on value
4. Conditionally rendering the stuff inside ng-container or using the template marked with #other

Here's a stackblitz demonstrating the above!

As an aside, I recognize my example is using Observable instead of Promises. As I understand it, they essentially work the same. However, I strongly recommend using Observables over Promises in any Angular application. Observables are far more flexible and I think you'll run into far less confusing behavior.