There are a couple of ways that one can control this depending upon your exact needs.
1. If it is to require the field to have a value before closing, simply mark the required attribute for that field to "On Close"; any fields that have no value, but are required upon close will be prompted to be filled-in before closing the incident is allowed.
2. If you have a more complicated situation consider a Rule that is triggered upon Incident close, along with other conditions. Such rule(s) can launch an in-product script which can perform further checks if desired. Should the script determine that close should not be allowed it can call:
helper.fail('Your desired message here')and the transaction will not be allowed, with the end-user receiving a pop-up message containing the message yuou have configured within your script.
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Marty James
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