This is the workaround suggested by Apple:
- (BOOL)__isValidResumeData:(NSData *)data{
if (!data || [data length] < 1) return NO;
NSError *error;
NSDictionary *resumeDictionary = [NSPropertyListSerialization propertyListWithData:data options:NSPropertyListImmutable format:NULL error:&error];
if (!resumeDictionary || error) return NO;
NSString *localFilePath = [resumeDictionary objectForKey:@"NSURLSessionResumeInfoLocalPath"];
if ([localFilePath length] < 1) return NO;
return [[NSFileManager defaultManager] fileExistsAtPath:localFilePath];
}
Edit (iOS 7.1 is not NDA'd anymore): I got this from a Twitter exchange with an Apple engineer, he suggested what to do, and I wrote the above implementation