After the last update when a newly created user tries to set his password the following error occurs:

500: Interner Serverfehler - User::checkPasswordStrength(): Argument #1 ($password) must be of type string, null given, called in xxx www/application/controllers/admin/Authentication.php on line 239

Reason is the Line:
$passwordStrengthError = $user->checkPasswordStrength($passwordTest) !== '';
which should read
$passwordStrengthError = $user->checkPasswordStrength($password) !== '';

However,
Yii::app()->setFlashMessage(sprintf(gT('Password cannot be blank and must fulfill minimum requirements: %s'), $passwordStrengthError), 'error');
Only shows "Password cannot be blank and must fulfill minimum requirements: 1" since $passwordStrengthError is a boolean

At least one other user is stumbled across this
https://forums.limesurvey.org/forum/installation-a-update-issues/156775-limesurvey-version-6-8-2-reset-password-error#268195