How to specify an interface/type as an @Input() in Storybook?

If it is just a string, boolean, etc, I would just add as an empty value or whatever value I want, like so:

export const Default = Template.bind({});
Default.args = {
  id: 'checkbox1',
  isChecked: false,
  isDisabled: false,
  isInline: false,
  isRequired: false,
  label: 'Test Checkbox'
};

But what about much more complicated types like FormGroup and AbstractControl in Angular Reactive Forms, for example?:

export const Default = Template.bind({});
Default.args = {
  checkboxAbstractControl: ??? (is of type 'AbstractControl'),
  parentFormGroup: ??? (is of type 'FormGroup',
};

From a documentation standpoint, how do I let the end user know that this is of type AbstractControl specifically, without having to resort to something clumsy like populating it with a string that says 'AbstractControl' for example?