How to use the @ng-dynamic-forms/core.isString function in @ng-dynamic-forms/core

get hasLabel(): boolean {
        return this.model.type !== DYNAMIC_FORM_CONTROL_TYPE_CHECKBOX && this.componentType !== DynamicKendoInputComponent && isString(this.model.label);
    }

get hasHint(): boolean {
        return this.isTextBox && isString((this.model as DynamicFormValueControlModel).hint);
    }

get hasLabel(): boolean {
        return this.model.type !== DYNAMIC_FORM_CONTROL_TYPE_CHECKBOX && this.componentType !== DynamicKendoInputComponent && isString(this.model.label);
    }

get hasHint(): boolean {
        return this.isTextBox && isString((this.model as DynamicFormValueControlModel).hint);
    }