I'm trying to use The library (dav4android) in another project for reading icloud calendar.
first i want to get the home set with propfind method:

dav.propfind(0, CalendarHomeSet.NAME, CalendarProxyReadFor.NAME, CalendarProxyWriteFor.NAME,GroupMembership.NAME);

the response from server is fine:

--> PROPFIND https://p01-caldav.icloud.com/xxxxxxxxxx/principal/ http/1.1
Content-Type: application/xml; charset=utf-8
Content-Length: 360
Depth: 0
<?xml version='1.0' encoding='UTF-8' ?><propfind xmlns="DAV:" xmlns:CAL="urn:ietf:params:xml:ns:caldav" xmlns:CARD="urn:ietf:params:xml:ns:carddav"><prop><CAL:calendar-home-set /><n0:calendar-proxy-read-for xmlns:n0="http://calendarserver.org/ns/" /><n1:calendar-proxy-write-for xmlns:n1="http://calendarserver.org/ns/" /><group-membership /></prop></propfind>
--> END PROPFIND (360-byte body)
<-- 207 Multi-Status https://p01-caldav.icloud.com/xxxxxxxxxx/principal/ (1244ms)
Server: AppleHttpServer/1dad28f
Date: Tue, 04 Apr 2017 05:12:01 GMT
Content-Type: text/xml
Transfer-Encoding: chunked
Connection: keep-alive
DAV: 1, access-control, calendar-access, calendar-schedule, calendar-auto-schedule, calendar-audit, calendar-managed-attachments, calendarserver-sharing, calendarserver-subscribed, calendarserver-home-sync
Accept-Ranges: bytes
X-Responding-Server: caldav:34201401:mr26p42ic-ztdg05121701:8001:17B34:9c2802d
X-Transaction-Id: 7a307730-c062-47de-94e5-192f3a7a7f2d
Vary: accept-encoding
Strict-Transport-Security: max-age=31536000; includeSubDomains
via: icloudedge:br30p01ic-zteu01123101:7401:17AE4:Berlin
X-Apple-Request-UUID: 7a307730-c062-47de-94e5-192f3a7a7f2d
access-control-expose-headers: X-Apple-Request-UUID
access-control-expose-headers: Via
<?xml version='1.0' encoding='UTF-8'?>
<multistatus xmlns='DAV:'>
<response>
<href>/8413061492/principal/</href>
<propstat>
<prop>
<calendar-home-set xmlns='urn:ietf:params:xml:ns:caldav'>
<href xmlns='DAV:'>https://p42-caldav.icloud.com:443/xxxxxxxxxx/calendars/</href>
</calendar-home-set>
<group-membership/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
</multistatus>
<-- END HTTP (473-byte body)

But i get this log and the home set is empty:

parseMultiStatus_Prop: Ignoring unknown property calendar-home-set(urn:ietf:params:xml:ns:caldav)
parseMultiStatus_Prop: Ignoring unknown property group-membership(DAV:)

i don't know what went wrong, but any help would be appreciated.
tnx in advance.

EDIT:
I realized that at.bitfire.dav4android.PropertyRegistry#factories is empty, BUT why?