So I have a modal with a form in my application, there are certain mandatory fields and then there are optional fields like external attendees which have 3 input boxes each for name, mail, and phone, the user fills it only if there are any external attendees. so what I wanna do now is let's say the user enters a value in the external name field but left out the email and number field empty then I wanna show an error message during form submissions,Anyone knows how i can do this?