You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: upgradeseries.go
    path of file: ./repos/juju/api/common
    
    the code of the file until where you have to start completion: // Copyright 2018 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package common

import (
	"github.com/juju/errors"
	"github.com/juju/names/v5"

	"github.com/juju/juju/api/base"
	apiwatcher "github.com/juju/juju/api/watcher"
	apiservererrors "github.com/juju/juju/apiserver/errors"
	"github.com/juju/juju/core/model"
	"github.com/juju/juju/core/watcher"
	"github.com/juju/juju/rpc/params"
)

// UpgradeSeriesAPI provides common
    
func (u *UpgradeSeriesAPI) UpgradeSeriesUnitStatus() (model.UpgradeSeriesStatus, string, error) {
	var results params.UpgradeSeriesStatusResults
	args := params.Entities{
		Entities: []params.Entity{{Tag: u.tag.String()}},
	}

	err := u.facade.FacadeCall("UpgradeSeriesUnitStatus", args, &results)
	if err != nil {
		return "", "", err
	}
	if len(results.Results) != 1 {
		return "", "", errors.Errorf("expected 1 result, got %d", len(results.Results))
	}

	res := results.Results[0]
	if res.Error != nil {
		// TODO (externalreality) The code to convert api errors (with
		// error codes) back to normal Go errors is in bad spot and
		// causes import cycles which is why we don't use it here and may
		// be the reason why it has few uses despite being useful.
		if params.IsCodeNotFound(res.Error) {
			return "", "", errors.NewNotFound(res.Error, "")
		}
		return "", "", res.Error
	}

	return res.Status, res.Target, nil
}