The isValid method throws if the form does not contain any validation attributes

Hi,

I am using a function that calls `ValidationService.isValid` on every page on my site, but some pages do not have any validated fields. When called on a form with no fields that have validation, I would expect the return value to be `true`. Instead, the method throws on this line: ` var invalidFormInputUIDs = formInputUIDs.filter(...)` with the error `formInputUIDs is undefined`.