Problem with multiselect usergroup when user already exists

[wtfred]

Hello,

Using femanager 7.2.1, there is a problem with usergroup as multiselect.

Step to reproduce:

• create a registration form with username and usergroup
• override Usergroup.html template to render the "multiselect" section
• try to register a user that is already existing

=> if you don't select any group, you have the expected error message
=> if you select at least one usergroup, then you have a Core Exception

"PHP Warning: Array to string conversion in /var/www/html/vendor/typo3fluid/fluid/src/Core/ViewHelper/TagBuilder.php line 200"

[pixeldesu]

I tried replicating this in Femanager v8 and I indeed got an error while doing so, which wasn't exactly related to the error above but might have the similar cause.

If you updated the Usergroup.html partial to work with multiple groups using the multiple="true" attribute, then you also need to remove the [0] from the name attribute of the same ViewHelper. Because if you only change to multiple you are now transmitting an array inside an array of usergroups, which multiple parts of TYPO3 probably have an issue with handling (in my case it's the PropertyMapper)

Could your error maybe be related to this?