[ical4j 4.x] `NullPointerException` in `JtxICalObject.extractProperties()`

[cketti]

Prerequisites:

• Have jtx Board installed and allow DAVx5 access to it
• Use the ical4j 4.x-enabled version of DAVx5 from https://github.com/bitfireAT/davx5-ose/tree/use-ical4j-4x

Steps to reproduce:

1. Click "add account".
2. Select "advanced login" option.
3. Enter cal.aegee.org as base URL, leave username and password empty.
4. Finish account setup.
5. Enable "OMS" in "CalDAV" tab.
6. Initial sync should work fine.
7. Manually re-sync → NullPointerException

Stacktrace:

java.lang.NullPointerException: Attempt to invoke virtual method 'byte[] java.nio.ByteBuffer.array()' on a null object reference
	at at.bitfire.ical4android.JtxICalObject$Companion.extractProperties(JtxICalObject.kt:504)
	at at.bitfire.ical4android.JtxICalObject$Companion.fromReader(JtxICalObject.kt:319)
	at at.bitfire.davdroid.sync.JtxSyncManager.processICalObject$core(JtxSyncManager.kt:175)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invokeSuspend$lambda$0$0$0(JtxSyncManager.kt:155)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.$r8$lambda$CuGlkJ9wW6_seOsk7DNaV_xSS40(Unknown Source:0)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2$$ExternalSyntheticLambda0.invoke(D8$$SyntheticClass:0)
	at at.bitfire.davdroid.sync.SyncException$Companion$wrapWithRemoteResource$1.invokeSuspend$suspendConversion0(SyncException.kt:43)
	at at.bitfire.davdroid.sync.SyncException$Companion$wrapWithRemoteResource$1.access$invokeSuspend$suspendConversion0(Unknown Source:0)
	at at.bitfire.davdroid.sync.SyncException$Companion$wrapWithRemoteResource$1$1.invoke(SyncException.kt:43)
	at at.bitfire.davdroid.sync.SyncException$Companion$wrapWithRemoteResource$1$1.invoke(SyncException.kt:43)
	at at.bitfire.davdroid.sync.SyncException$Companion.wrapWithRemoteResourceSuspending(SyncException.kt:48)
	at at.bitfire.davdroid.sync.SyncException$Companion$wrapWithRemoteResource$1.invokeSuspend(SyncException.kt:43)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:263)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:94)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:70)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source:1)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:48)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source:1)
	at at.bitfire.davdroid.sync.SyncException$Companion.wrapWithRemoteResource(SyncException.kt:42)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invokeSuspend$lambda$0$0(JtxSyncManager.kt:140)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.$r8$lambda$MKOfwgC7oDWikMawDoBFRNJQEWk(Unknown Source:0)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2$$ExternalSyntheticLambda2.onResponse(D8$$SyntheticClass:0)
	at at.bitfire.dav4jvm.okhttp.Response$Companion.parse(Response.kt:221)
	at at.bitfire.dav4jvm.okhttp.DavResource.processMultiStatus$parseMultiStatus(DavResource.kt:802)
	at at.bitfire.dav4jvm.okhttp.DavResource.processMultiStatus(DavResource.kt:821)
	at at.bitfire.dav4jvm.okhttp.DavResource.processMultiStatus(DavResource.kt:772)
	at at.bitfire.dav4jvm.okhttp.DavCalendar.multiget(DavCalendar.kt:178)
	at at.bitfire.dav4jvm.okhttp.DavCalendar.multiget$default(DavCalendar.kt:142)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invokeSuspend$lambda$0(JtxSyncManager.kt:138)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)
	at kotlinx.coroutines.InterruptibleKt.runInterruptibleInExpectedContext(Interruptible.kt:48)
	at kotlinx.coroutines.InterruptibleKt.access$runInterruptibleInExpectedContext(Interruptible.kt:1)
	at kotlinx.coroutines.InterruptibleKt$runInterruptible$2.invokeSuspend(Interruptible.kt:40)
	at kotlinx.coroutines.InterruptibleKt$runInterruptible$2.invoke(Unknown Source:8)
	at kotlinx.coroutines.InterruptibleKt$runInterruptible$2.invoke(Unknown Source:4)
	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndspatched(Undispatched.kt:66)
	at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:43)
	at kotlinx.coroutines.BuildersKt__Builders_commonKt.withContext(Builders.common.kt:157)
	at kotlinx.coroutines.BuildersKt.withContext(Unknown Source:1)
  	at kotlinx.coroutines.InterruptibleKt.runInterruptible(Interruptible.kt:39)
	at kotlinx.coroutines.InterruptibleKt.runInterruptible$default(Interruptible.kt:36)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invokeSuspend(JtxSyncManager.kt:137)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invoke(Unknown Source:8)
	at at.bitfire.davdroid.sync.JtxSyncManager$downloadRemote$2.invoke(Unknown Source:2)
	at at.bitfire.davdroid.sync.SyncException$Companion.wrapWithRemoteResourceSuspending(SyncException.kt:48)
	at at.bitfire.davdroid.sync.JtxSyncManager.downloadRemote(JtxSyncManager.kt:136)
	at at.bitfire.davdroid.sync.SyncManager$syncRemote$2$download$1.invokeSuspend(SyncManager.kt:605)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)