I've seen this once or twice before. Is it a bug or what? Game works normally though.
There's also a "ButtonSelfRenderErrors.txt" in "C:\Program Files (x86)\Steam\steamapps\common\ai war fleet command\RuntimeData".
Please do report those whenever you see them
There's been an extremely intermittent null-bug popping around inside the game-button (the ones used for the buy/tech menus, etc) render code for like a couple years, and I've never been able to reproduce it, and errors from the distributed version of the game don't give line numbers (probably the second thing I most miss from the pre-Unity version), and it's a loooong method. So I've added more and more debug info that it dumps when it hits an exception in there and this is the first time I've seen a log since I added the last bit.
Thankfully, your log tells me that there was something wrong with rendering a tech button (debug step 18), and that it's probably because the button's "Tag" was null instead of something convertible to a TechType. Why on earth that would happen, I don't know. I'll change it to just early-out of the render process for that button in that case in the future, and see what happens. Maybe you'll see a blank tech button, or the button will stop drawing altogether when it realizes it's not valid, etc.
Anyway, thanks for the report