I ran into an issue, which I am not able to solve myself. In my Lovelace frontend GUI, when adding a new card, the “card chooser menu” is empty. See screenshot:
I tried this on multiple browser (incl. Incognito), but it does not seem to be a cache-issue.
Does anybody have tips on troubleshooting, etc.? 
I’ve got the same issue today after doing some dashoard editing. No card shown at all, tried different browsers too. No idea at all where to go from here?
Ok, just solved it for me. Going to the raw configuration editor, there was a NULL line, commented that out, and all back again.
Thanks for posting your solution. Had the same issue and wasted hours this morning trying to correct it until I came across your post! Surely this has to be a bug (or undocumented feature! lol) and not by design?
