2.1.40: A network error occurred. Error details: error decoding response body: missing field mod at line 1 column 99

[dreamflasher]

Desktop version: 2.1.40
AnkiDroid: 2.14.6
anki-sync-server: 41205c0 on 3 Feb 2020

AnkiDroid with that anki-sync-server runs smoothly, showing me that the server is running correctly, as well as the AnkiDroid client config.

With Anki Desktop I get the error that the username/password is wrong and after clicking ok, another error message: A network error occurred. Error details: error decoding response body: missing field mod at line 1 column 99
But only if I apply the changes suggested here: #85 which looks like a PR that should be merged. ping @tsudoko (then I see that the desktop client communicates with the server from the server log, else it doesn't connect at all)