[midPoint] Question regarding custom failure message in password policy

[Sven Feyerabend]

Hi everyone,

I'm currently trying to implement a password policy using the 
checkExpression feature.
To notify the user what went wrong in case of failure, I set the value 
of failureMessage, which the docs describe as follows:

Message that will be displayed to user when the expression check fails.

When my expression fails however, the error message looks like this:

[Warning: Property for 'Änderung des Passwortes ist fehlgeschlagen: 
Provided password does not satisfy the policies: MY_CUSTOM_MESSAGE' not 
found]

This makes me think, that the property is expected to hold some kind of 
reference to a String that can then be displayed.
Can someone clarify the usage of this mechanism?

Thanks in advance!

Kind regards

Sven