23A - Can we display warning message to highlight duplicate offers in Offer screen?

Summary:

As part of 23A Autocomplete Rules - Extend Rules for Job Offer - We can write rules to validate if the candidate has other job applications in a specific phase and state. An example could be to write a rule to block multiple offers for a candidate. This would completely block recruiters proceeding with offer creation. Can we write rules to display warning message but allow users to proceed with offer creation on a case to case basis?

Content (required):

We used Field Modification Rule to trigger warning message instead of displaying error message. We started getting null pointer exception error. Is there a way to fix this null pointer exception error?