The terms you'll want to read up on are JIT speculation and deoptimisation. There's a whole range of things that can be done like trapping the null derefrence i

The terms you'll want to read up on are JIT speculation and deoptimisation. There's a whole range of things that can be done like trapping the null derefrence instead of an explicit check, once hot code is inlined the check could be lifted out several call frames outside of loops. Then you can ignore the check later. All sortsa stuff can happen.