DAV sync broken while calling java.util.TimeZone java.util.Calendar.getTimeZone()

[albancrommer]

Server: Nextcloud 23.0.5 via DAVx⁵
Store : Fdroid
Tasks Client: 12.7 
Device: Samsung S7
Android: 8.0.0

Expected behavior

The tasks should be updated from/to the server

Observed behavior

The tasks sync fails silently

Error message

Found on the app > Settings > (accounts) DAVx⁵ page

Error: Attempt to invoke virtual method 'java.util.TimeZone java.util.Calendar.getTimeZone()' on a null object reference

Context

Hi, and of course thanks a lot for tasks!

After an upgrade of the app, it stopped synchronizing. The server works alright cf. access log

<IP> - <user> [11/Jul/2022:13:52:23 +0000] "PROPFIND /remote.php/dav/calendars/<user>/calendar/ HTTP/1.1" 207 319 "-" "DAVx5/4.2.2-gplay (2022/06/21; dav4jvm; okhttp/4.9.3) Android/8.0.0"

Old phone, so I guess that's the problem.