addCondition:labelled:

addCondition:labelled does not seem to be working the way I expected. I just want to validate that a given text field is not empty I have a description definition method and setter: descriptionTags ^MAStringDescription new selectorAccessor: #tagsConverter; label: 'Tags'; priority: 40; addCondition: [:value | value notEmpty ] labelled: 'Please provide at least one tag'; yourself tagsConverter: aString tags := aString asUppercase subStrings asSet On submit, I get an error that nil does not understand asUppercase. Shouldn't the condition fail before the setter is called? I've tried [ :value | value notNil ], and beRequired as well, got the same error. I also tried to change the initialize method of the object I'm describing to set tags to an empty collection but that didn't work either. Thanks, Joel