validation of radio buttons

[Andy Keyworth]

I'm trying to make a simple radio button validate: we just have to know if the user has selected something from the group. I keep trying to set the JQL query for the validator to

%{17900} != null

and define the validation as "current issue belongs to output of the query"

But when set like this, even if a radio button/option is selected, the validation fails, and the error message still displays. What is the criteria, if not null?

[Udo Brand]

In JQL you find Radio Buttons with any value with this syntax

<RadioButtonName> is not empty