XF 2.1 cannot start new category node

[🔥Iggy🔥]

hello,
this bug we suffered since importing from vb over a year and a half ago.....or...well....actually not at first, but perhaps around the time of the 2.1 upgrade....

cannot create new category node...gives error

ErrorException: [E_WARNING] implode(): Invalid arguments passed in src/XF/Mvc/Entity/ValueFormatter.php at line 103

1. XF::handlePhpError()
2. implode() in src/XF/Mvc/Entity/ValueFormatter.php at line 103
3. XF\Mvc\Entity\ValueFormatter->encodeValueForSource() in src/XF/Mvc/Entity/Manager.php at line 782
4. XF\Mvc\Entity\Manager->encodeValueForSource() in src/XF/Mvc/Entity/Entity.php at line 1456
5. XF\Mvc\Entity\Entity->_saveToSource() in src/XF/Mvc/Entity/Entity.php at line 1195
6. XF\Mvc\Entity\Entity->save() in src/XF/Mvc/FormAction.php at line 69
7. XF\Mvc\FormAction->XF\Mvc\{closure}() in src/XF/Mvc/FormAction.php at line 187
8. XF\Mvc\FormAction->run() in src/XF/Admin/Controller/AbstractNode.php at line 110
9. XF\Admin\Controller\AbstractNode->actionSave() in src/XF/Mvc/Dispatcher.php at line 350
10. XF\Mvc\Dispatcher->dispatchClass() in src/XF/Mvc/Dispatcher.php at line 257
11. XF\Mvc\Dispatcher->dispatchFromMatch() in src/XF/Mvc/Dispatcher.php at line 113
12. XF\Mvc\Dispatcher->dispatchLoop() in src/XF/Mvc/Dispatcher.php at line 55
13. XF\Mvc\Dispatcher->run() in src/XF/App.php at line 2184
14. XF\App->run() in src/XF.php at line 391
15. XF::runApp() in admin.php at line 13

any ideas here? be nice to make a category....was sort of hoping i wouldnt ever want to again haha but then now of course we need one...

thank you