For me in Game dev, codex has a habit of checking every argument for null and then silently early exiting the methods when true. I have explicit instructions for it not to do this - but it still does. I haven't done any c# outside game dev but I have no idea why people would want their programs to silently fail.
And this is why having null in the type system is better.
Same; I explicitly added an instruction in AGENTS.md to tell it that sometimes it's better to crash if something crucial is missing at runtime, but it keeps insisting on checking for null references and other invalid values.
It's better if I don't let it generate code and just use it for reviewing my code.