Add JUEL expression , but add [" and "] around the expression.

i.e.  +String Value ->  ["${provisioningContext.contextData['TrackingAreaCodes']}"]

This saves , but after it's not possible to download the template or to select that VFC instance from the Properties page.  The property can be accessed from the composition page, where the value can be altered.

The JUEL expression should be validated at Save time, and give user indication of error cause.