Error while testing the dev tutorial

hi, im new to nextcloud and the dev part. so i setup a nextcloud dev enviroment and want to try the tutorial

i am at the point: i set the NoteController, route.php and the Db Migration like the tutorial describes. In the meanwhile i had to do a update for nextcloud.
Now i want to activate the app at the nextcloud page and i get the following error msg in browser debug console:
appId: “ownnotes”

error: TypeError
columnNumber: 13190
fileName: “http://localhost/nextcloud/settings/js/vue-settings-apps-users-management.js
lineNumber: 67
message: “ is undefined”

and in the nextcloud.log:

{"reqId":"XJC4VARl13v7wPcSBKW1","level":3,"time":"2019-07-22T11:17:04+00:00","remoteAddr":"","user":"admin","app":"PHP","method":"POST","url":"\/nextcloud\/index.php\/settings\/apps\/enable","message":"Cannot declare class OCA\\Notes\\Migration\\Version000000Date20190722131302, because the name is already in use at \/var\/www\/html\/nextcloud\/apps\/ownnotes\/lib\/Migration\/Version000000Date20190722131302.php#0","userAgent":"Mozilla\/5.0 (X11; Ubuntu; Linux x86_64; rv:68.0) Gecko\/20100101 Firefox\/68.0","version":""}

what exactly is the problem?

Just a quick update. The app tutorial has gotten an overall refresh so it should now work nicely again with Nextcloud 17