Right - I believe with the right documentation, this shouldn't be a problem.
Everyone hates NSNull because ObjC developers love to message nils.

The last option is to add a counterpart to -map , mapWithOptions that'd have something like

```
OSMapOptionsUseNSNullForNil
OSMapOptionsCrashOnNil
OSMapOptionsAvoidNil
```

but at the end of the day - it's about keeping the lib as small as possible and providing users with sane defaults. Not sure how i'd feel about adding options.