Not possible to import LDAP users into another LDAP directory using Directory Imported (argument credential cannot be null)

Steps to Reproduce

1. Create a Delegated LDAP directory in Crowd
2. Login using any LDAP user(s) into Crowd, so that these users and their groups are copied to Crowd's database
3. Create another duplicate Delegated LDAP Directory with the same exact settings as the LDAP directory created earlier
4. Navigate to Crowd >> Users >> Import Users >> Directory Importer
5. Set the Source Directory as the Delegated LDAP Directory created earlier (with the users), and Destination Directory as the duplicate Delegated LDAP Directory with no users in it. Try to import.

This will always fail with this exception:

2012-08-29 21:16:26,793 http-8240-5 ERROR [console.action.dataimport.DirectoryConfirmation] java.lang.IllegalArgumentException: argument credential cannot be null
com.atlassian.crowd.importer.exceptions.ImporterException: java.lang.IllegalArgumentException: argument credential cannot be null

Why this is important

Some of our customers need to duplicate their delegated directory users to another directory which can be used for testing. Asking the users to login manually for each of the user, just to get their data copied to the DB is definitely a daunting task, which can be avoided, if the import is successful