I'd like to implement a pre-filled Description field for any project using a certain workflow, so I set up a Behaviour based on the Screen ID of the Create Issue screen for that workflow. However, it's not working. If I remove the screen ID check, it works as expected on all screens, but that's not what I want 
def desc = getFieldById("description")
def descDefaultValue = """blah""".replaceAll(/ /, '')
if (FieldScreen.getId() == 12903) {
if (! underlyingIssue?.description) {
desc.setFormValue(descDefaultValue)
}
}
Apologies in advance if I missed something simple. Thanks for the feedback.