title: Argument of type 'unknown[]' is not assignable to parameter of type > 'OperatorFunction
body: <p><em>component.ts</em></p>
  <p><code>initialize()</code> method says</p>
  <blockquote>
  <p>Argument of type 'unknown[]' is not assignable to parameter of type
  'OperatorFunction&lt;unknown[], unknown&gt;'.   Type 'unknown[]' provides no
  match for the signature '(source: Observable&lt;unknown[]&gt;):
  Observable'</p>
  </blockquote>
  <pre><code>alertsChanged$: Observable&lt;AlertModel[]&gt;;
  
  private initialize(): void {
    
  
      this.alertsChanged$ = this.alertsService.getAlerts().pipe(
        map((res) =&gt; res), // here it returns the above error
        tap((res) =&gt; {
          
          this.setDataForFilters(res); //Argument of type 'unknown' is not assignable to parameter of type 'AlertModel[]'.  
         
        }),          
      );
    }
  
   private setDataForFilters(alerts: AlertModel[]): void {}
  </code></pre>
  <p><em>service.ts</em></p>
  <pre><code> // no issues here
  
   getAlerts(): Observable&lt;AlertModel[]&gt; {
        return this.angularFireDatabase
        .list&lt;AlertModel&gt;(`groups/${this.groupId}/alerts`)
        .valueChanges()
        .pipe(
          map((res) =&gt; orderBy(res, ['timeStamp'], ['desc'])),
          first()
        );
    }
  </code></pre>
  <p><em>.html</em></p>
  <pre><code> &lt;app-alerts
      [alerts]=&quot;alertsChanged$ | async&quot;
    &gt;&lt;/app-alerts&gt;
  </code></pre>
  <p>Please let me the issue here?</p>