docs: def _upgrade(self):
          """
          Upgrade the serialized object if necessary.
  
          Raises:
              FutureVersionError: file was written by a future version of the
                  software.
          """
          logging.debug("[FeedbackCalibration]._upgrade()")
          version = Version.fromstring(self.version)
          logging.debug('[FeedbackCalibration] version=%s, class_version=%s',
                        str(version), self.class_version)
          if version > Version.fromstring(self.class_version):
              logging.debug('[FeedbackCalibration] version>class_version')
              raise FutureVersionError(Version.fromstring(self.class_version),
                                       version)
          elif version < Version.fromstring(self.class_version):
              if version < Version(0, 1):
                  self._c_filler = None
                  self._c_drop = None
                  self.version = str(Version(0, 1))
              if version < Version(0, 2):
                  self.hw_version = Version(1)
                  self.version = str(Version(0, 2))
                  logging.info('[FeedbackCalibration] upgrade to version %s',
                               self.version)
              if version < Version(0, 2):
                  self.hw_version = Version(1)
                  self.version = str(Version(0, 2))
                  logging.info('[FeedbackCalibration] upgrade to version %s',
                               self.version)
              if version < Version(0, 3):
                  self.version = str(Version(0, 3))
                  logging.info('[FeedbackCalibration] upgrade to version %s',
                               self.version)