yel-dspace-angular/src/app/process-page/form/process-parameters/parameter-value-input/string-value-input/string-value-input.component.html

<input required #string="ngModel" type="text" name="string-value-{{index}}" class="form-control" id="string-value-{{index}}" [ngModel]="value" (ngModelChange)="setValue($event)"/>
<div *ngIf="string.invalid && (string.dirty || string.touched)"
     class="alert alert-danger validation-error">
    <div *ngIf="string.errors.required">
        {{'process.new.parameter.string.required' | translate}}
    </div>
</div>