Null is garbage and responsible for billions of dollars worth of net loss. I wouldn't list null as one of his achievements.
Speaking at a software conference in 2009, Tony Hoare apologized for inventing the null reference:
"I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years."
You would think that a logical statement standing by itself and alone would lead to a logical reaction, but no. People respond to authority not to logic. So instead of listing why null is bad here, I just reference tony himself.
So yeah even Tony wouldn't like null listed there as an achievement.
People don't like being told they are wrong.
Why don't read most of the threads here. Most claims are unwarranted. People vote based off there gut and whether they agree with it, it has nothing to do with substantiated evidence.
Most people here don't know how bad the concept of null is so they voted based off of that, never knowing that the inventor of null dislikes the concept himself.
Also keep in mind, Tony's claim itself has no evidence. He never lists why null is bad. His claim is unwarranted, but his reputation precedes him. You as others do vote based off of emotion and are unable to admit it.
Let's not get too pedantic. The way I said it obviously implies that the OP listed null as an achievement. Similar to how the OP listing null alongside an achievement can imply it's an achievement.
People don't vote based off of correctness. They vote based off of emotion. Emotion tells them I don't have the authority to say negative things about Tony. Even though I said nothing negative, Tony agrees with what I said.