Completly ignore exceptions without original instance time (RECURRENCE-ID)

Author: rfc2822

lib/src/androidTest/kotlin/at/bitfire/synctools/mapping/calendar/LegacyAndroidEventProcessorTest.kt

@@ -1023,4 +1023,30 @@ class LegacyAndroidEventProcessorTest {
         }
     }
 
+    @Test
+    fun testPopulateException_Exdate_NoRecurrenceId() {
+        populateException({
+            put(Events._SYNC_ID, "testPopulateException_AllDay")
+            put(Events.TITLE, "Recurring all-day event with cancelled exception and no RECURRENCE-ID")
+            put(Events.DTSTART, 1594056600000L)
+            put(Events.EVENT_TIMEZONE, tzVienna.id)
+            put(Events.ALL_DAY, 0)
+            put(Events.RRULE, "FREQ=DAILY;COUNT=10")
+        }, {
+            put(Events.ORIGINAL_SYNC_ID, "testPopulateException_AllDay")
+            //put(Events.ORIGINAL_INSTANCE_TIME, 1594143000000L)
+            put(Events.ORIGINAL_ALL_DAY, 0)
+            put(Events.DTSTART, 1594143000000L)
+            put(Events.ALL_DAY, 0)
+            put(Events.EVENT_TIMEZONE, tzShanghai.id)
+            put(Events.STATUS, Events.STATUS_CANCELED)
+        }).let { event ->
+            assertEquals("Recurring all-day event with cancelled exception and no RECURRENCE-ID", event.summary)
+            assertEquals(DtStart("20200706T193000", tzVienna), event.dtStart)
+            assertEquals("FREQ=DAILY;COUNT=10", event.rRules.first().value)
+            assertTrue(event.exDates.isEmpty())
+            assertTrue(event.exceptions.isEmpty())
+        }
+    }
+
 }

lib/src/main/kotlin/at/bitfire/synctools/mapping/calendar/LegacyAndroidEventProcessor.kt

@@ -409,12 +409,14 @@ class LegacyAndroidEventProcessor(
         for (exception in exceptions) {
             val exceptionEvent = Event()
 
+            // exceptions are required to have a RECURRENCE-ID
+            val recurrenceId = exceptionEvent.recurrenceId ?: continue
+
             // convert exception row to Event
             populateEvent(exception, to = exceptionEvent)
 
             // generate EXDATE instead of RECURRENCE-ID exceptions for cancelled instances
-            val recurrenceId = exceptionEvent.recurrenceId
-            if (exceptionEvent.status == Status.VEVENT_CANCELLED && recurrenceId != null) {
+            if (exceptionEvent.status == Status.VEVENT_CANCELLED) {
                 val list = DateList(
                     if (DateUtils.isDate(recurrenceId)) Value.DATE else Value.DATE_TIME,
                     recurrenceId.timeZone