alt Hacker NewsMostly though if you do anything with the returned value at the call site you need to change that code anyways? If it is not just passing it on, and even then you might need to adapt its signatures. E.g. if you change from String | Null to String you remove the null handling. If you add Null you need to add Null handling?
No that's not right.
If you were calling a function which might return null (String | Null), you will already have null handling at the call site, but if you now change that function such that it never returns null (String), you still have the (now unnecessary) null handling, but this doesn't hurt and you don't have to change anything at the call site.
Likewise, if you were passing a String to a function that doesn't accept null (String), the call site already made sure that the parameter isn't null, and if you change the function so that it does now accept null (String | Null), again nothing needs to be changed at the call site.