title: Argument of type 'string' is not assignable to parameter of type 'AbstractControl'. Angular Reactive Forms
body: <p>I am trying to push a string value into a formArray using material forms, however it is returning this error: </p>
  
  <pre><code>Argument of type 'string' is not assignable to parameter of type 'AbstractControl'.
  </code></pre>
  
  <p>If I try and push a full object into the array it works fine, but as a string value it doesn't. This is where I declare the formArray: </p>
  
  <pre><code>this.maintenanceFormGroup = this._formBuilder.group({
        title: '',
        description: ['', Validators.required],
        maintenance_images_url: this._formBuilder.array([]),
    });
  </code></pre>
  
  <p>and this is where I try and push the string value(s) into the array: </p>
  
  <pre><code>  const pushDownloadUrlIntoMaintenancePhotosArray = flatMap(() =&gt; {
        return this._storage.downloadURL
          .map(url =&gt; {
            console.log(url)
            const controls = &lt;FormArray&gt;this.formGroup.controls.maintenance_images_url;
            controls.push(url);
          });
      });
  </code></pre>
  
  <p>Any suggestion as to why I am getting this error? </p>