just came to say i have the same problem
E/DatabaseUtils(27501): Writing exception to parcel
E/DatabaseUtils(27501): android.database.sqlite.SQLiteConstraintException: contacts.pinned may not be NULL (code 19)
E/DatabaseUtils(27501): at android.database.sqlite.SQLiteConnection.nativeExecute(Native Method)
E/DatabaseUtils(27501): at android.database.sqlite.SQLiteConnection.execute(SQLiteConnection.java:555)
E/DatabaseUtils(27501): at android.database.sqlite.SQLiteSession.execute(SQLiteSession.java:619)
E/DatabaseUtils(27501): at android.database.sqlite.SQLiteStatement.execute(SQLiteStatement.java:44)
E/DatabaseUtils(27501): at com.android.providers.contacts.aggregation.ContactAggregator.updatePinned(ContactAggregator.java:2373)
E/DatabaseUtils(27501): at com.android.providers.contacts.ContactsProvider2.updateRawContact(ContactsProvider2.java:4414)
E/DatabaseUtils(27501): at com.android.providers.contacts.ContactsProvider2.updateRawContacts(ContactsProvider2.java:4322)
E/DatabaseUtils(27501): at com.android.providers.contacts.ContactsProvider2.updateInTransaction(ContactsProvider2.java:3975)
E/DatabaseUtils(27501): at com.android.providers.contacts.AbstractContactsProvider.update(AbstractContactsProvider.java:166)
E/DatabaseUtils(27501): at com.android.providers.contacts.ContactsProvider2.update(ContactsProvider2.java:2138)
E/DatabaseUtils(27501): at android.content.ContentProviderOperation.apply(ContentProviderOperation.java:225)
E/DatabaseUtils(27501): at com.android.providers.contacts.AbstractContactsProvider.applyBatch(AbstractContactsProvider.java:237)
E/DatabaseUtils(27501): at com.android.providers.contacts.ContactsProvider2.applyBatch(ContactsProvider2.java:2250)
E/DatabaseUtils(27501): at android.content.ContentProvider$Transport.applyBatch(ContentProvider.java:260)
E/DatabaseUtils(27501): at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:192)
E/DatabaseUtils(27501): at android.os.Binder.execTransact(Binder.java:404)
E/DatabaseUtils(27501): at dalvik.system.NativeStart.run(Native Method)
D/davdroid.DavSyncAdapter(31735): Closing httpClient
E/AndroidRuntime(31735): FATAL EXCEPTION: SyncAdapterThread-1
E/AndroidRuntime(31735): Process: at.bitfire.davdroid:sync, PID: 31735
E/AndroidRuntime(31735): android.database.sqlite.SQLiteConstraintException: contacts.pinned may not be NULL (code 19)
E/AndroidRuntime(31735): at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:173)
E/AndroidRuntime(31735): at android.database.DatabaseUtils.readExceptionWithOperationApplicationExceptionFromParcel(DatabaseUtils.java:160)
E/AndroidRuntime(31735): at android.content.ContentProviderProxy.applyBatch(ContentProviderNative.java:519)
E/AndroidRuntime(31735): at android.content.ContentProviderClient.applyBatch(ContentProviderClient.java:377)
E/AndroidRuntime(31735): at at.bitfire.davdroid.resource.LocalCollection.commit(LocalCollection.java:311)
E/AndroidRuntime(31735): at at.bitfire.davdroid.resource.LocalAddressBook.commit(LocalAddressBook.java:148)
E/AndroidRuntime(31735): at at.bitfire.davdroid.syncadapter.SyncManager.pullChanged(SyncManager.java:208)
E/AndroidRuntime(31735): at at.bitfire.davdroid.syncadapter.SyncManager.synchronize(SyncManager.java:89)
E/AndroidRuntime(31735): at at.bitfire.davdroid.syncadapter.DavSyncAdapter.onPerformSync(DavSyncAdapter.java:134)
E/AndroidRuntime(31735): at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:259)