Registration app 0.3.0 error after update

Hi guys, I just upgraded from Nextcloud 12.0.1 to 12.0.2. Everything was ok except Registration app to version 0.3. I got this error:
An exception occurred while executing ‘ALTER TABLE oc_registration ADD “username” VARCHAR(255) NOT NULL’: SQLSTATE[23502]: Not null violation: 7 ERROR: column “username” contains null values

Anyone got an idea to fix it ? I love registration much

My specs:
Ubuntu 16.04.03
PHP 7.0

Thanks in advance.

wanna take a look here? Registration app 0.3.0 issue

and maybe this answer as well? Registration app 0.3.0 issue