We've got safety checks that we do right before saving the file to ensure we aren't saving bad data. In this case we were about to save the user with a blank password, which would cause the user to break. This error is that safety check kicking in and it reports where in the code the issue likely came from. I would make a new ticket and send this stacktrace and maybe a copy of the config file.
The good news is that the user should not be broken as we DIDNT save the file to disk, but the bad news it appears there is a bug attempting to clearing data on a user.
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com