[fw-general] isValid not executed on multicheckbox when the element is not required and value is not set

[Guillaume ORIOL]

Here is a schematic view of the form I have:
(*) choice 1
    [X] option 1
    [_] option 2
    [_] option 3
( ) choice 2
When "choice 1" is checked, at least one of the three options should be 
checked.
I wanted to write a specific validator for the options but...
as the "options" multi-checkbox is not required (as they are ignored if 
choice 2 is checked), when no option is checked, the validator is not 
executed at all.

Does anybody have a solution for it?

Thanks
--

Guillaume ORIOL