An error that may be surprisingly addictive. Or rather, it is already stuck.
It seems to occur often due to errors in SQL statements, but the error I'm seeing now is not using SQL statements.
Then, I found a suspicious place.
It was just a spelling mistake!
My reference method in $this? showed that Response was Repsponse. Fixed and successfully resolved.
If you're having trouble, you might want to look at yourself with var_dump($this).