check NULL repeat_interval instead of zero

app/src/main/kotlin/com/simplemobiletools/calendar/helpers/DBHelper.kt

@@ -366,7 +366,7 @@ class DBHelper private constructor(val context: Context) : SQLiteOpenHelper(cont
     fun getEventsInBackground(fromTS: Int, toTS: Int, callback: (events: MutableList<Event>) -> Unit) {
         val events = ArrayList<Event>()
 
-        val selection = "$COL_START_TS <= ? AND $COL_END_TS >= ? AND $COL_REPEAT_INTERVAL IS 0"
+        val selection = "$COL_START_TS <= ? AND $COL_END_TS >= ? AND $COL_REPEAT_INTERVAL IS NULL"
         val selectionArgs = arrayOf(toTS.toString(), fromTS.toString())
         val cursor = getEventsCursor(selection, selectionArgs)
         events.addAll(fillEvents(cursor))