This error is expected (as designed) in the context of a transition with a condition using a parameter that does not exist since the condition is not defined and cannot be evaluated.
As the error says…Controller 'thing': Transition '' in state 'test' uses parameter '' which does not exist in controller.”
You need to create a Parameter before adding a Condition in order to avoid this error.
You can create the Parameter after having created to Condition, but you will also need to assign it using the pull-down list of the Condition, in this case.
In both of the above scenarios, the error will no longer exist once the invalide condition is resolved.
The error is trying to help you understand what does not work in the condition logic.