Well no, the key difference between null and floating point is that for all its flaws, floating point is by far the fastest way of doing non-integer numerical c

Well no, the key difference between null and floating point is that for all its flaws, floating point is by far the fastest way of doing non-integer numerical computation. Null is just an ugly convenience hack of arguable merit, floats are fundamental. They're not a major source of error when you're implementing a model which is already inexact to a far larger degree than the problems caused by floats. Black-Scholes does not perfectly price an option, your bootstrapped curve is not a perfect predictor of market conditions in 28 years time. These are the problems faced in front-office finance, the error is already so far beyond 1 + 0.1 not perfectly matching 1.1 that it's not worth caring about. I've worked on applications where users just wanted to see numbers to the nearest 100k so they could model out a few trades they planned to make over the phone. When you're working on a retail banking app where you need to track customer's balances, or an accounting system, or anything like that, then sure, floating point would be malpractice. That is nothing like any of the applications I've worked on in the financial field.