Yes, it seems like both @eastgate 's code and @mwra 's slightly simpler code work. Also in my larger Zettelkasten. I guess it may be a bad idea to assign badges for both type and this warning for empty fields (text and attributes), or what do you both think? I have found nice badges for each purpose, so if there are no direct issues with it, I like to try it. A good thing with Tinderbox is that it is possible to change later, without too much hassle…
These AgentQueries are a real test of logical reasoning… I may be a university professor, but this I need to practice 
Thanks again for all help!