[gav]

I've worked on a lot of legacy Java code where these kind of null checks cause problems. The end up confusing things in corner cases.

You should verify arguments at a top level, then let the code underneath blow up with a NullPointerException if something unexpected happened. Your stack trace will point at where the problem lies.

I find for some reason that a lot of people want to use null instead of empty lists where you'll end up with this ugliness:

    if (list != null) {
        for (Thing t: list) {
            processThing(t);
        }
    }

Instead of just passing in a Collections.emptyList() instead.

[barrkel]

I agree with one exception: if you're storing the value passed down into a structure which will survive the call, then the value should be checked for null before being placed in the structure. This is because the eventual null pointer exception may occur long after it was put in the structure, obscuring how it got there.