It’s not. The fact that it’s got a ? means a developer explicitly marked it and told you it’s nullable. The lack of a mark means you have to consider it nullab

It’s not. The fact that it’s got a ? means a developer explicitly marked it and told you it’s nullable. The lack of a mark means you have to consider it nullable but no one has told you that setting it to null is the right thing. Things may still go wrong if you set it null though. It’s just the contract isn’t explicit in the code.