[O] org-caldav issue (wrong-type-argument stringp nil)

[Bertrand SIMON]

I use the ELPA version of the package with emacs 25 and nextcloud.
When I Launch the sync. I get the lisp message:
`(wrong-type-argument stringp nil)`

I have to mention that I have already modified the org-caldav.el file 
according to this message: 
(https://lists.gnu.org/archive/html/emacs-orgmode/2014-11/msg00423.html).

The *org-caldav-debug* says:

` ========== Started sync.
Syncing first calendar entry:
(:calendar-id "MY-CALENDAR-ID" :files ("MY-PATH-TO-ORG-CALENDARFILE") 
:inbox ("MY-PATH-TO-ORG-CALENDARFILE"))
Check connection for 
https://ncloud.zaclys.com/remote.php/dav/calendars/MY-USER-ID/MY-CALENDAR-ID/.
Generating ICS file /tmp/org-caldav-438wKX.`

and... that's all...


any idea ?

Thanks for your help.
--
Bertrand Simon