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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 get_signing_serializer(self, app: 'Quart') -> Optional[URLSafeTimedSerializer]: """Return a serializer for the session that also signs data. This will return None if the app is not configured for secrets. """

        if not app.secret_key:
            return None

        options = {
            'key_derivation': self.key_derivation,
            'digest_method': self.digest_method,
        }
        return URLSafeTimedSerializer(
            app.secret_key, salt=self.salt, serializer=self.serializer, signer_kwargs=options,
        )