<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _sync_to_disk(self):
 """Write any changes made on Refpkg to disk. Other methods of Refpkg that alter the contents of the package will call this method themselves. Generally you should never have to call it by hand. The only exception would be if another program has changed the Refpkg on disk while your program is running and you want to force your version over it. Otherwise it should only be called by other methods of refpkg. """

        with self.open_manifest('w') as h:
            json.dump(self.contents, h, indent=4)
            h.write('\n')