I have made a custom form field for liferay CE 7.2 like this example:
https://github.com/natocesarrego/slider

My custom form field is a customized fileupload field. 

Liferay forms builder has some validation and required settings by default. 
How do I implement my custom field into this existing liferay form validation?

I want to achieve that if my fileupload field is empty and it is set to required in the settings the user can not submit the form.