I am trying to make use of `-[NSObject autoContentAccessingProxy]` as described at <http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/nsobject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/autoContentAccessingProxy>.

The object I am trying to proxy implements the `NSDiscardableContent` protocol and `-autoContentAccessingProxy` successfully returns a non-nil value.

If, however, I try to send a message to the proxy, I always get an `NSInvalidArgumentException` with a reason of "\*\*\* -[NSProxy methodSignatureForSelector:] called!".

I understand that if I was writing my own `NSProxy`-based class, I would have to implement the `-methodSignatureForSelector:` method, but in this case, I am not writing the proxy, just trying to use the proxy provided by the documented method. For what it's worth, I can see that the proxy is actually of type `NSAutoContentAccessingProxy`, so I would expect that that class would indeed have an implementation for `-methodSignatureForSelector:`.

Here is a small block of code using an NSPurgeableData instance instead of my custom class. This small block has exactly the same issue.

```
NSPurgeableData * data = [NSPurgeableData dataWithBytes:"123" length:3];
NSLog(@"data.length = %u", data.length);
id proxyData = [data autoContentAccessingProxy];
NSLog(@"proxyData.length = %u", [proxyData length]);    //  throws NSInvalidArgumentException!
[data endContentAccess];
[data release];

```

Do I have some misunderstanding of the `-autoContentAccessingProxy` method here, or is it just completely broken?