code: def asset_versions(self):
          
          if self._asset_versions is None:
              self._asset_versions = AssetVersionList(
                  self._version,
                  service_sid=self._solution['service_sid'],
                  asset_sid=self._solution['sid'],
              )
          return self._asset_versions
docs: Access the asset_versions
  
          :returns: twilio.rest.serverless.v1.service.asset.asset_version.AssetVersionList
          :rtype: twilio.rest.serverless.v1.service.asset.asset_version.AssetVersionList