message: diabled add files, if no files are selected
diff: <mat-dialog-actions *ngIf="isDialog">
  <button mat-raised-button color="primary"
  + [disabled]="!selectedFiles.length"
  [mat-dialog-close]="selectedFiles" >
  <mat-icon>add</mat-icon>
  {{ 'unit.addFilesToUnit' | translate }}
  