Using the Users app, you can create a record with an invalid date, wreaking all sorts of havoc.
Steps to Reproduce:
On folio-snapshot, create a user with the birth date 0000-01-01 (yes, seems unlikely, but we've seen it happen twice in a production system, obviously user error).
User is created with birth date 0000-01-01
An error is returned indicating that the user cannot be created, BUT the user is actually created, with the value +0000-01-01T00:00:00.000+00:00 in the personal.dateOfBirth property. The user cannot be edited, pulled up in the UI, or retrieved via API. The API returns this error when you try to retrieve the record:
As a side effect, the /users/expire/timer API will be broken if this user ever expires, as the module will be unable to process the retrieved user record for the same reason and will log an NPE and the connection will hang open until eventually mod-users has 1000 connections open to Okapi and no more can be opened, effectively crashing the system.