Cannot specify default (blank) Logon Application for the Chris21 Agent in the UI

In the Chris21 Agent form in the UNIFYBroker UI the "Logon Application" field is mandatory:

However the help for the the field says it can be left blank to not include it in the logon:

I was able to workaround this by editing the Agent configuration XML directly, to remove the value.  When I did so the value passed to Chris21 defaulted to "chris21".  So another workaround is likely to be entering "chris21" into the field directly rather than leaving it blank.

UNIFYBroker v5.3.2.0
Chris21 Connector v5.3.0.0