code: def upgrade_juju(
              self, dry_run=False, reset_previous_upgrade=False,
              upload_tools=False, version=None):
          
          raise NotImplementedError()
docs: Upgrade Juju on all machines in a model.
  
          :param bool dry_run: Don't do the actual upgrade
          :param bool reset_previous_upgrade: Clear the previous (incomplete)
              upgrade status
          :param bool upload_tools: Upload local version of tools
          :param str version: Upgrade to a specific version