Nothing happens when changing to ActionVariable in ActionNode if there are no variables

[RailKill]

Version: 2.2.2
Severity: Low

Steps to Reproduce

1. Create an ActionNode without first creating a variable in RootNode.
2. Change the type to ActionVariable.

Current Behavior

It doesn't show controls for setting variables.

Expected Behavior

The UI should at least update, and the dropdown shall be empty. Not updating the UI just because there are no variables feels unresponsive.

[RailKill]

ActionVariable now selectable in ActionNode even without variables.