Steps to replicate:
- create new user including password
- make administrator
- assign all surveys
- edit user: remove administator right + remove all surveys
- add regular role + survey through surveys box --> save + logout
- next log in as new user: error StrongTypingException("The value for column \'Password\' in table \'Users\' is DBNull."
The password seems to have been removed. Once added again the error does not show anymore.