Found this issue when trying to add a translation webinterface to my project
http://jmsyst.com/bundles/JMSTranslationBundle/master/webinterface
Following all the steps there and pointing your browser to [your_dev]/_trans, we have a warning saying

ContextErrorException: Warning: Illegal offset type in isset or empty in [...]/vendor/ezsystems/ezpublish-kernel/eZ/Publish/Core/MVC/Legacy/Templating/LegacyEngine.php line 136

I think is because for some reason, this bundle passes a TemplateReference object to this method and so the illegal offset type is thrown