WARN , token.TokenService, unexpected error while cleaning expired stored tokens: null

Periodic error received in Self Service Password Reset log.   The error repeats hourly.

java.lang.Throwable
    at password.pwm.util.localdb.LocalDBDataStore.size(LocalDBDataStore.java:107)
    at password.pwm.svc.token.DataStoreTokenMachine.size(DataStoreTokenMachine.java:190)
    at password.pwm.svc.token.DataStoreTokenMachine.cleanup(DataStoreTokenMachine.java:73)
    at password.pwm.svc.token.TokenService$CleanerTask.run(TokenService.java:403)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)

There is an issue with the Security Key SSPR is using.
Settings ⇨ Security ⇨ Application Security ⇨ Security Key

Before making any changes, backup your current SSPR configuration using the Download Configuration option in Configuration Manager.

Enter Configuration Editor and go to:  Settings ⇨ Security ⇨ Application Security ⇨ Security Key

1.   Click Clear Value, then OK to Clear password for setting Security Key.

2.   Click Store Value, then Generate Random  to generate a random key/password.   Copy that key to the confirm password field, and click Store Password  to store the password.

3.   Save the changes in Configuration Editor.

Monitor the logs and the error should be gone.