Hi ,
well since i was not able to upgrade my 4.8 project i started a 4.9 project from scratch, i used the 4.8 plugin in the 4.9 project while not 4.9.2 was released, when 4.9.2 was released i downloaded the updated plugin and got these errors
i can not count how often i restarted from scratch 
if you want i can give you access to our SVN Team Server so you can look into this