OK I figured it out. I assumed that there wasn't actually a "critical OS file missing", so if it couldn't write to /dev/null it was probably permissions. So I changed permissions to 666 for /dev/null and it works fine now.
So my question now is, what are implications of setting /dev/null to 666? It's basically a black hole yes? So doing this won't affect security? Excuse my ignorance, but I'm newish to Linux...