I've deleted all TemplateMonster theme files and it's still showing in the Design configuration page.
Process completed to remove themes:
- Remove theme files from app/design/frontend
- Clear static file cache
- Remove from var/
There's also Testing Custom Theme that shows two instances for reason, but in app/design/frontend there's only one. (I've cleared static file cache)
Fatal error: Call to a member function getId() on null in vendor/magento/framework/View/Model/Layout/Merge.php on line 751
– Mex Lane Jul 13 '16 at 10:42