Media Library gives null reference exception

My development kentico 12 enviroment is acting funny. every time i open the media selector, and click on the media libraries tab, i get a null reference exception. (media library ID is 0).

Only on an item, where an image has previously already been selected, will the media libraries tab open correctly. unless i click on that tab again, it again will give the same null reference exception.

I cant find anything on this issue. Its also only happening on my development enviroment, and nobody else has this issue, nor an idea how to fix it. so im a bit stuck, and would like to understand why this is happening