Old thread, old problem, same here 🙁
Now that I got used on my 1st RF camera, it is daily business to get it out of the bag and... forget the cap!
It doesn't even help that the compact Ricoh's have the light meter on the lens, because it was an available light situation, where the meter in the viewer displays < F2.8 even if the cap were off.
Lesson learned. Will buy a filter next weekend!
(amusing thread, anyway)