same hier... since 5.7.1.20221122-1 nightly build update we see plenty of 501 error messages upon calendar sync in OSX Calendar or Thunderbird. From Web-Gui there are no problems.

Nov 23 12:43:55 sogod [460386]: |SOGo| starting method 'REPORT' on uri '/SOGo/dav/user%40domain/Calendar/personal/'
Nov 23 12:43:55 sogod [460386]: |SOGo| traverse: user@domain => Calendar => personal
Nov 23 12:43:55 sogod [460386]: |SOGo|   do traverse name: 'user@domain'
Nov 23 12:43:55 sogod [460386]: |SOGo|   do traverse name: 'Calendar'
Nov 23 12:43:55 sogod [460386]: |SOGo|   do traverse name: 'personal'
2022-11-23 12:43:55.065 sogod[460386:460386] <MySQL4Channel[0x0x55911e0ba800] connection=0x0x55911e0baf70> SQL: SELECT c_path4 FROM sogo_folder_info WHERE c_path2 = 'user@domain' AND c_folder_type = 'Appointment';
2022-11-23 12:43:55.066 sogod[460386:460386] <MySQL4Channel[0x0x55911e0ba800] connection=0x0x55911e0baf70>   query has results, entering fetch-mode.
Nov 23 12:43:55 sogod [460386]: |SOGo| set clientObject: <0x55911e01af50[SOGoAppointmentFolder]: name=personal container=0x55911d9724b0/Calendar ocs=/Users/user@domain/Calendar/personal>
2022-11-23 12:43:55.069 sogod[460386:460386] <MySQL4Channel[0x0x55911dfe2910] connection=0x0x55911df8d8a0> SQL: SELECT b.c_name,a.c_component,b.c_version FROM sogo_quick_appointment a, sogo_store b WHERE (a.c_folder_id = 5 AND b.c_folder_id = 5) AND (((c_startdate IS NULL) OR (c_startdate <= 1670374861)) AND ((c_enddate IS NULL) OR (c_enddate >= 1668560461)) AND (c_component = 'vevent') AND (c_iscycle = '0')) AND a.c_name = b.c_name AND (c_deleted != 1 OR c_deleted IS NULL);
2022-11-23 12:43:55.071 sogod[460386:460386] <MySQL4Channel[0x0x55911dfe2910] connection=0x0x55911df8d8a0>   query has results, entering fetch-mode.
2022-11-23 12:43:55.072 sogod[460386:460386] EXCEPTION: <NSException: 0x55911de46b60> NAME:NSInvalidArgumentException REASON:[NSString+stringWithUTF8String:]: NULL cString INFO:(null)
Nov 23 12:43:55 sogod [460386]: |SOGo| request took 0.011173 seconds to execute
Nov 23 12:43:55 sogod [460386]: 116.202.27.247 "REPORT /SOGo/dav/user@domain/Calendar/personal/ HTTP/1.0" 501 0/413 0.013 - - 0 - 14

Could you kindly review the last changes in nightly build?

I can confirm this bug was introduced by commit https://github.com/Alinto/sogo/commit/c62b043e26111ee4d6073b9b37931e15f3b95753, in file SoObjects/SOGo/SOGoContentObject.m. Specifically:

  data = [objectRecord objectForKey: @"c_content"];
  if (data && [data isKindOfClass: [NSString class]])
    ASSIGN (content, data);
  else
    ASSIGN (content, [NSString stringWithUTF8String:[data bytes]]);

You can see, that if data is NULL, it will be passed to stringWithUTF8String, which will raise the exception. This is a very critical error, and I'm a bit surprised this wasn't caught during testing...

Thanks for reporting the issue. This is nightly build and is by definition unstable.
Issue has been fixed in https://github.com/Alinto/sogo/commit/27860648c18a3557b5eeacc0999a95dfd9ff63d8

Sebastien