NSKeyedUnarchiver - try/catch needed?

As I understand, the use of @try/@catch blocks is discouraged, because exceptions should only be thrown at unrecoverable, catastrophic errors (refer to this discussion with a nice answer by @bbum: Exception Handeling in iOS).

So I looked through my code and found a @try/@catch block that I don't know how to get rid of:

NSData *fileData = [NSData dataWithContentsOfFile: ....];

NSDictionary *dictionary;

@try {
   dictionary = [NSKeyedUnarchiver unarchiveObjectWithData: fileData];
}
@catch (NSException *exception) {
   //....
}
@finally {
  //...
}

The problem is that (as stated in the documentation) +unarchiveObjectWithData: raises an NSInvalidArchiveOperationException if the NSData doesn't contain a valid archive.

Since the data is provided by a file the user chose, it is not guaranteed that it contains a valid archive, and thus the application would crash if a incorrect file was chosen.

Now two questions:

1. Why doesnt +unarchiveObjectWithData: just return nil (Edit: and an NSError**) if the archive is not valid (this doesn't seem to qualify as a catastrophic or unrecoverable error).
2. Is the pattern above correct (using @try)? I have found no method that lets us check if the data contains a valid archive beforehand and have found no possibility to handle this case using the delegate protocol. Antyhing I overlooked?

Note that the code above of course works, I just wonder if its the best practice.<