since suffering the same I felt to not duplicate that topic …
In the middle of using the automation wizzard at the stage ‘trigger’ in yaml mode (for an enocean switch)
event_data: [254, 229, 15, 156]
Error was thrown after I felt to press the ‘SAVE’ button which I did hoping it would end up with a sensefull explanation telling me about what I need to define inside the conditions section.
Instead I was served by that error which is of no help.
Granted if you ask about my experience with automation within HA. 0,00% since there’s a 1000 topics about that but I still wasn’t able to located the one named "automation for dummies, an easy step-by-step explanation where everything’s explained line by line.
And yes automation.yaml is 0 bytes in size at my end since I never managed to get a single automating up and running, let it be old-style non-UI-created or using the wizzard. (not enough braincells perhaps)
Anyway I do rate it likely that the error thrown isn’t ideal. Hope this explanation helps to turn it into something more sensefull.