The AllNullableTypes nullable enum field, which is

  AnEnum? aNullableEnum;

generates

@property(nonatomic, assign) AnEnum aNullableEnum;

That can't express a null value. Currently what happens is you get whatever 0 maps to in the enum, which is wrong.

IIRC @gaaclarke and I have discussed this in the past; using NSNumber like we do for other numeric types means clients have to cast, which isn't great. Options I can see include:

• Use a sentinel value corresponding to null, but we'd have to be careful about naming collisions. (I think this was suggested at the time, I forget whether there are other problems we discussed with that approach.)
• Generating a wrapper class in the case of a nullable enum, that would behave sort of like C++'s std::optional.