'Refresh the current state from the backing file.
If the backing file has never been read before (indicated by checking
self._backing_file_initialized) it will merge the file with the
in-memory state, rather than overwriting it.'

def _read_from_backing_file(self):

    if self._backing_file:
        merge_backing_file = (not self._backing_file_initialized)
        self.read_from_file(self._backing_file, merge=merge_backing_file)
        self._backing_file_initialized = True
