Guard against NULL issue in default mapper

[vokal-isaac]

It's in or around

        Class managedObjectClass = objc_getClass(className);
        objc_property_t prop = class_getProperty(managedObjectClass, propertyName);

        NSString *attributeString = [NSString stringWithCString:property_getAttributes(prop) encoding:NSUTF8StringEncoding];

in expectedClassForObject:andKey:. (I think it's that prop is NULL and then property_getAttributes(prop) crashes.)

[designatednerd]

@vokal-isaac Would you consider this addressed by #49?

[vokal-isaac]

Maybe? #49 sticks an assertion on that, so it'll give useful information in debugging, but it'll still crash here in a release build. I'm not sure I can think of a sane set of circumstances that would cause this to happen in a release build and not in a debug build, but I haven't tried too hard yet.

[designatednerd]

@vokal-isaac I'm inclined to close this one out unless it crops its ugly head up again. Agreed?

[vokal-isaac]

Assign it to me (_edit_ I can't actually assign it, since I don't own this repo) and I'll spend a bit of time actually thinking about it today, and either close it based on what's already done or implement a resolution.

[designatednerd]

@vokal-isaac: Done. I think you should at least be able to close it from here.