10.2: Remove user from a group results in an error

[cortho]

Steps to reproduce

1. In the Users page add any user to any group
2. Remove the group for this user
3. The togglegroups.php AJAX call results with status: error
4. In the JS console you will read response.data is undefined
5. The user count in the group list at the left side is not reduced

Expected behaviour

No errors, the group list ist correctly updated

Actual behaviour

The AJAX call results in a status error breaking functionality in users.js when there is no response

Server configuration

Operating system:
Ubuntu 18.04.2 LTS

Web server:
apache2-2.4.29-1ubuntu4.6

Database:
mariadb-server-10.1 10.1.38-0ubuntu0.18.04.2

PHP version:
7.2.17-0ubuntu0.18.04.1

ownCloud version: (see ownCloud admin page)
10.2.0.5

Updated from an older ownCloud or fresh install:
fresh install

Where did you install ownCloud from:
owncloud.org download page

Are you using external storage, if yes which one: local/smb/sftp/...
no

Are you using encryption: yes/no
no

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/...
no

Client configuration

Browser:
Firefox 66.0.4

Operating system:
Ubuntu 18.04.2 LTS

Logs

Web server error log

no errors

ownCloud log (data/owncloud.log)

no errors

Browser log

see attached Screenshot

[davitol]

Tested in 10.2 and it is reproducible. Not reproducible in 10.1 so it is a regression

@cortho Refreshing the browser the group count shows the right number of users, does it happen to you too?

[cortho]

@davitol Yes, by refreshing the browser the correct count is shown.

I found this issue because one of our apps hooks in this functionality and is expecting a non-erroneous response from the ajax, when there was no error.

[micbar]

@pmaier1 Regression found. No breaking anything directly, but need reloading the page.

[pmaier1]

Yes, please plan fixing @micbar.

[micbar]

Fix in owncloud-archive/user_management#188

[micbar]

Introduced in https://github.com/owncloud/enterprise/issues/2598

[sharidas]

PR's created against branches:

• master branch Fix response when user is removed from group owncloud-archive/user_management#188
• core release-10.2.1 branch [10.2.1] Backport to Fix response when user is removed from group #35570
• stable10 [stable10] Backport to Fix response when user is removed from group #35571