Granted, this is a stupid question but it's a case of understanding the words but not the meaning.
The documentation for the loadMetaData function in NSIncrementalStore states:
Any subclass of NSIncrementalStore which is file-based must be able to handle being initialized with a URL pointing to a zero-length file. This serves as an indicator that a new store is to be constructed at the specified location and allows applications using the store to securely create reservation files in known locations.
How are you supposed to handle a zero-length file? How would you recognise a zero length file? Are you not supposed to just create a (database) file or directory at the specified NSURL location?