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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate_flushed(self) -> None: """ Will raise an exception if there are some changes made since the last persist. """

        journal_diff = self._journal_storage.diff()
        if len(journal_diff) > 0:
            raise ValidationError(
                "StorageDB had a dirty journal when it needed to be clean: %r" % journal_diff
            )