Best practice for validating null value of non required UIInput

[Jan Bols]

I have a form containing (among others) a field to fill in a company name  
and fields to fill in the address of the company (street, nr, bus, zip,  
city, country). I want to give an error message when the user fills one of  
the address fileds but not the company name.

The way I solved the problem was to add a custom validator to each address  
field that checks the submitted value of the company name for a null  
value. This works but the validation occurs on every address field.

Is there another way to do this?

Jan