diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index a648396f9..80fb2b2dc 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -34,8 +34,8 @@ android {
     defaultConfig {
         testApplicationId = "org.tasks.test"
         applicationId = "org.tasks"
-        versionCode = 607
-        versionName = "6.8.1"
+        versionCode = 608
+        versionName = "6.9"
         targetSdkVersion(Versions.targetSdk)
         minSdkVersion(Versions.minSdk)
         multiDexEnabled = true
diff --git a/app/src/androidTest/java/org/tasks/data/CaldavDaoTests.java b/app/src/androidTest/java/org/tasks/data/CaldavDaoTests.java
new file mode 100644
index 000000000..725f90457
--- /dev/null
+++ b/app/src/androidTest/java/org/tasks/data/CaldavDaoTests.java
@@ -0,0 +1,63 @@
+package org.tasks.data;
+
+import static com.natpryce.makeiteasy.MakeItEasy.with;
+import static java.util.Collections.singletonList;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.tasks.makers.TagDataMaker.newTagData;
+import static org.tasks.makers.TagMaker.TAGDATA;
+import static org.tasks.makers.TagMaker.TASK;
+import static org.tasks.makers.TagMaker.newTag;
+import static org.tasks.makers.TaskMaker.ID;
+import static org.tasks.makers.TaskMaker.newTask;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.todoroo.astrid.dao.TaskDao;
+import com.todoroo.astrid.data.Task;
+import javax.inject.Inject;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+public class CaldavDaoTests {
+  @Inject TaskDao taskDao;
+  @Inject TagDao tagDao;
+  @Inject TagDataDao tagDataDao;
+  @Inject CaldavDao caldavDao;
+
+  @Test
+  public void getCaldavTasksWithTags() {
+    Task task = newTask(with(ID, 1L));
+    taskDao.createNew(task);
+    TagData one = newTagData();
+    TagData two = newTagData();
+    tagDataDao.createNew(one);
+    tagDataDao.createNew(two);
+    tagDao.insert(newTag(with(TASK, task), with(TAGDATA, one)));
+    tagDao.insert(newTag(with(TASK, task), with(TAGDATA, two)));
+    caldavDao.insert(new CaldavTask(task.getId(), "calendar"));
+
+    assertEquals(singletonList(task.getId()), caldavDao.getTasksWithTags());
+  }
+
+  @Test
+  public void ignoreNonCaldavTaskWithTags() {
+    Task task = newTask(with(ID, 1L));
+    taskDao.createNew(task);
+    TagData tag = newTagData();
+    tagDataDao.createNew(tag);
+    tagDao.insert(newTag(with(TASK, task), with(TAGDATA, tag)));
+
+    assertTrue(caldavDao.getTasksWithTags().isEmpty());
+  }
+
+  @Test
+  public void ignoreCaldavTaskWithoutTags() {
+    Task task = newTask(with(ID, 1L));
+    taskDao.createNew(task);
+    tagDataDao.createNew(newTagData());
+    caldavDao.insert(new CaldavTask(task.getId(), "calendar"));
+
+    assertTrue(caldavDao.getTasksWithTags().isEmpty());
+  }
+}
diff --git a/app/src/main/java/com/todoroo/astrid/dao/TaskDao.java b/app/src/main/java/com/todoroo/astrid/dao/TaskDao.java
index 2b45865fa..c2136b4fb 100644
--- a/app/src/main/java/com/todoroo/astrid/dao/TaskDao.java
+++ b/app/src/main/java/com/todoroo/astrid/dao/TaskDao.java
@@ -142,6 +142,9 @@ public abstract class TaskDao {
   @RawQuery(observedEntities = {Task.class, GoogleTask.class, CaldavTask.class, Tag.class})
   public abstract DataSource.Factory<Integer, TaskContainer> getTaskFactory(SimpleSQLiteQuery query);
 
+  @Query("UPDATE tasks SET modified = datetime('now', 'localtime') WHERE _id in (:ids)")
+  public abstract void touch(List<Long> ids);
+
   /**
    * Saves the given task to the database.getDatabase(). Task must already exist. Returns true on
    * success.
diff --git a/app/src/main/java/com/todoroo/astrid/service/Upgrader.java b/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
index 1ab2e408f..eafaaaca0 100644
--- a/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
+++ b/app/src/main/java/com/todoroo/astrid/service/Upgrader.java
@@ -1,6 +1,7 @@
 package com.todoroo.astrid.service;
 
 import static com.google.common.base.Strings.isNullOrEmpty;
+import static org.tasks.db.DbUtils.batch;
 
 import android.os.Environment;
 import com.google.common.base.Strings;
@@ -9,12 +10,16 @@ import com.google.common.collect.ImmutableListMultimap;
 import com.google.common.collect.ListMultimap;
 import com.google.common.collect.Multimaps;
 import com.todoroo.astrid.api.GtasksFilter;
+import com.todoroo.astrid.dao.TaskDao;
 import java.io.File;
 import java.util.List;
 import javax.inject.Inject;
 import org.tasks.R;
 import org.tasks.analytics.Tracker;
 import org.tasks.analytics.Tracking;
+import org.tasks.caldav.CaldavUtils;
+import org.tasks.data.CaldavDao;
+import org.tasks.data.CaldavTaskContainer;
 import org.tasks.data.Filter;
 import org.tasks.data.FilterDao;
 import org.tasks.data.GoogleTaskAccount;
@@ -41,6 +46,7 @@ public class Upgrader {
   private static final int V6_4 = 546;
   private static final int V6_7 = 585;
   private static final int V6_8_1 = 607;
+  private static final int V6_9 = 608;
   private final Preferences preferences;
   private final Tracker tracker;
   private final TagDataDao tagDataDao;
@@ -50,6 +56,8 @@ public class Upgrader {
   private final GoogleTaskListDao googleTaskListDao;
   private final UserActivityDao userActivityDao;
   private final TaskAttachmentDao taskAttachmentDao;
+  private final CaldavDao caldavDao;
+  private final TaskDao taskDao;
 
   @Inject
   public Upgrader(
@@ -61,7 +69,9 @@ public class Upgrader {
       DefaultFilterProvider defaultFilterProvider,
       GoogleTaskListDao googleTaskListDao,
       UserActivityDao userActivityDao,
-      TaskAttachmentDao taskAttachmentDao) {
+      TaskAttachmentDao taskAttachmentDao,
+      CaldavDao caldavDao,
+      TaskDao taskDao) {
     this.preferences = preferences;
     this.tracker = tracker;
     this.tagDataDao = tagDataDao;
@@ -71,6 +81,8 @@ public class Upgrader {
     this.googleTaskListDao = googleTaskListDao;
     this.userActivityDao = userActivityDao;
     this.taskAttachmentDao = taskAttachmentDao;
+    this.caldavDao = caldavDao;
+    this.taskDao = taskDao;
   }
 
   public void upgrade(int from, int to) {
@@ -83,6 +95,7 @@ public class Upgrader {
       run(from, V6_4, this::migrateUris);
       run(from, V6_7, this::migrateGoogleTaskFilters);
       run(from, V6_8_1, this::migrateCaldavFilters);
+      run(from, V6_9, this::applyCaldavCategories);
       tracker.reportEvent(Tracking.Events.UPGRADE, Integer.toString(from));
     }
     preferences.setCurrentVersion(to);
@@ -95,6 +108,18 @@ public class Upgrader {
     }
   }
 
+  private void applyCaldavCategories() {
+    List<Long> tasksWithTags = caldavDao.getTasksWithTags();
+    for (CaldavTaskContainer container : caldavDao.getTasks()) {
+      at.bitfire.ical4android.Task remoteTask =
+          CaldavUtils.fromVtodo(container.caldavTask.getVtodo());
+      if (remoteTask != null) {
+        tagDao.insert(container.task, CaldavUtils.getTags(tagDataDao, remoteTask.getCategories()));
+      }
+    }
+    batch(tasksWithTags, taskDao::touch);
+  }
+
   private void performMarshmallowMigration() {
     try {
       // preserve pre-marshmallow default backup location
diff --git a/app/src/main/java/com/todoroo/astrid/tags/TagsControlSet.java b/app/src/main/java/com/todoroo/astrid/tags/TagsControlSet.java
index 73ba0c707..3be3a85bc 100644
--- a/app/src/main/java/com/todoroo/astrid/tags/TagsControlSet.java
+++ b/app/src/main/java/com/todoroo/astrid/tags/TagsControlSet.java
@@ -6,10 +6,7 @@
 
 package com.todoroo.astrid.tags;
 
-import static com.google.common.collect.Iterables.transform;
-import static com.google.common.collect.Lists.newArrayList;
 import static com.google.common.collect.Lists.transform;
-import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.newHashSet;
 import static com.todoroo.andlib.utility.AndroidUtilities.atLeastJellybeanMR1;
 
@@ -48,7 +45,6 @@ import java.util.List;
 import java.util.Set;
 import javax.inject.Inject;
 import org.tasks.R;
-import org.tasks.data.Tag;
 import org.tasks.data.TagDao;
 import org.tasks.data.TagData;
 import org.tasks.data.TagDataDao;
@@ -366,22 +362,12 @@ public final class TagsControlSet extends TaskEditControlFragment {
   }
 
   private boolean synchronizeTags(Task task) {
-    long taskId = task.getId();
     for (TagData tagData : selectedTags) {
       if (Task.NO_UUID.equals(tagData.getRemoteId())) {
         tagDataDao.createNew(tagData);
       }
     }
-    Set<TagData> existing = newHashSet(tagDataDao.getTagDataForTask(taskId));
-    Set<TagData> selected = newHashSet(selectedTags);
-    Set<TagData> added = difference(selected, existing);
-    Set<TagData> removed = difference(existing, selected);
-    tagDao.deleteTags(taskId, newArrayList(transform(removed, TagData::getRemoteId)));
-    for (TagData tagData : added) {
-      Tag newLink = new Tag(task, tagData);
-      tagDao.insert(newLink);
-    }
-    return !removed.isEmpty() || !added.isEmpty();
+    return tagDao.applyTags(task, tagDataDao, selectedTags);
   }
 
   @Override
diff --git a/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java b/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
index 9d56de79a..196b800d7 100644
--- a/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
+++ b/app/src/main/java/org/tasks/caldav/CaldavSynchronizer.java
@@ -33,7 +33,6 @@ import com.todoroo.astrid.service.TaskCreator;
 import com.todoroo.astrid.service.TaskDeleter;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.StringReader;
 import java.net.ConnectException;
 import java.net.SocketTimeoutException;
 import java.net.UnknownHostException;
@@ -56,7 +55,6 @@ import org.tasks.data.CaldavAccount;
 import org.tasks.data.CaldavCalendar;
 import org.tasks.data.CaldavDao;
 import org.tasks.data.CaldavTask;
-import org.tasks.data.Tag;
 import org.tasks.data.TagDao;
 import org.tasks.data.TagData;
 import org.tasks.data.TagDataDao;
@@ -350,58 +348,37 @@ public class CaldavSynchronizer {
 
   private void processVTodo(
       String fileName, CaldavCalendar caldavCalendar, String eTag, String vtodo) {
-    List<at.bitfire.ical4android.Task> tasks =
-        at.bitfire.ical4android.Task.Companion.fromReader(new StringReader(vtodo));
-
-    if (tasks.size() == 1) {
-      at.bitfire.ical4android.Task remote = tasks.get(0);
-      Task task;
-      CaldavTask caldavTask = caldavDao.getTask(caldavCalendar.getUuid(), fileName);
-      if (caldavTask == null) {
-        task = taskCreator.createWithValues("");
-        taskDao.createNew(task);
-        caldavTask =
-            new CaldavTask(task.getId(), caldavCalendar.getUuid(), remote.getUid(), fileName);
-      } else {
-        task = taskDao.fetch(caldavTask.getTask());
-      }
-      CaldavConverter.apply(task, remote);
-      applyCategories(task, remote.getCategories());
-      task.putTransitory(SyncFlags.GTASKS_SUPPRESS_SYNC, true);
-      taskDao.save(task);
-      caldavTask.setVtodo(vtodo);
-      caldavTask.setEtag(eTag);
-      caldavTask.setLastSync(DateUtilities.now() + 1000L);
-      if (caldavTask.getId() == Task.NO_ID) {
-        caldavTask.setId(caldavDao.insert(caldavTask));
-        Timber.d("NEW %s", caldavTask);
-      } else {
-        caldavDao.update(caldavTask);
-        Timber.d("UPDATE %s", caldavTask);
-      }
-    } else {
-      Timber.e("Received VCALENDAR with %s VTODOs; ignoring %s", tasks.size(), fileName);
+
+    at.bitfire.ical4android.Task remote = CaldavUtils.fromVtodo(vtodo);
+    if (remote == null) {
+      Timber.e("Invalid VCALENDAR: %s", fileName);
+      return;
     }
-  }
 
-  private void applyCategories(Task task, List<String> categories) {
-    long taskId = task.getId();
-    List<TagData> selectedTags = tagDataDao.getTags(categories);
-    Set<String> toCreate =
-        difference(newHashSet(categories), newHashSet(transform(selectedTags, TagData::getName)));
-    for (String name : toCreate) {
-      TagData tag = new TagData(name);
-      tagDataDao.createNew(tag);
-      selectedTags.add(tag);
+    Task task;
+    CaldavTask caldavTask = caldavDao.getTask(caldavCalendar.getUuid(), fileName);
+    if (caldavTask == null) {
+      task = taskCreator.createWithValues("");
+      taskDao.createNew(task);
+      caldavTask =
+          new CaldavTask(task.getId(), caldavCalendar.getUuid(), remote.getUid(), fileName);
+    } else {
+      task = taskDao.fetch(caldavTask.getTask());
     }
-    Set<TagData> existing = newHashSet(tagDataDao.getTagDataForTask(taskId));
-    Set<TagData> selected = newHashSet(selectedTags);
-    Set<TagData> added = difference(selected, existing);
-    Set<TagData> removed = difference(existing, selected);
-    tagDao.deleteTags(taskId, newArrayList(Iterables.transform(removed, TagData::getRemoteId)));
-    for (TagData tagData : added) {
-      Tag newLink = new Tag(task, tagData);
-      tagDao.insert(newLink);
+    CaldavConverter.apply(task, remote);
+    tagDao.applyTags(task, tagDataDao, CaldavUtils.getTags(tagDataDao, remote.getCategories()));
+    task.putTransitory(SyncFlags.GTASKS_SUPPRESS_SYNC, true);
+    taskDao.save(task);
+    caldavTask.setVtodo(vtodo);
+    caldavTask.setEtag(eTag);
+    caldavTask.setLastSync(DateUtilities.now() + 1000L);
+    if (caldavTask.getId() == Task.NO_ID) {
+      caldavTask.setId(caldavDao.insert(caldavTask));
+      Timber.d("NEW %s", caldavTask);
+    } else {
+      caldavDao.update(caldavTask);
+      Timber.d("UPDATE %s", caldavTask);
     }
   }
+
 }
diff --git a/app/src/main/java/org/tasks/caldav/CaldavUtils.java b/app/src/main/java/org/tasks/caldav/CaldavUtils.java
new file mode 100644
index 000000000..920401e43
--- /dev/null
+++ b/app/src/main/java/org/tasks/caldav/CaldavUtils.java
@@ -0,0 +1,36 @@
+package org.tasks.caldav;
+
+import static com.google.common.collect.Lists.transform;
+import static com.google.common.collect.Sets.difference;
+import static com.google.common.collect.Sets.newHashSet;
+
+import androidx.annotation.Nullable;
+import java.io.StringReader;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import org.tasks.data.TagData;
+import org.tasks.data.TagDataDao;
+
+public class CaldavUtils {
+  public static @Nullable at.bitfire.ical4android.Task fromVtodo(String vtodo) {
+    List<at.bitfire.ical4android.Task> tasks =
+        at.bitfire.ical4android.Task.Companion.fromReader(new StringReader(vtodo));
+    return tasks.size() == 1 ? tasks.get(0) : null;
+  }
+
+  public static List<TagData> getTags(TagDataDao tagDataDao, List<String> categories) {
+    if (categories.isEmpty()) {
+      return Collections.emptyList();
+    }
+    List<TagData> selectedTags = tagDataDao.getTags(categories);
+    Set<String> toCreate =
+        difference(newHashSet(categories), newHashSet(transform(selectedTags, TagData::getName)));
+    for (String name : toCreate) {
+      TagData tag = new TagData(name);
+      tagDataDao.createNew(tag);
+      selectedTags.add(tag);
+    }
+    return selectedTags;
+  }
+}
diff --git a/app/src/main/java/org/tasks/data/CaldavDao.java b/app/src/main/java/org/tasks/data/CaldavDao.java
index d3c4b2634..e2cd3e5e9 100644
--- a/app/src/main/java/org/tasks/data/CaldavDao.java
+++ b/app/src/main/java/org/tasks/data/CaldavDao.java
@@ -64,6 +64,12 @@ public interface CaldavDao {
   @Query("SELECT * FROM caldav_tasks WHERE cd_task = :taskId")
   List<CaldavTask> getTasks(long taskId);
 
+  @Query(
+      "SELECT task.*, caldav_task.* FROM tasks AS task "
+          + "INNER JOIN caldav_tasks AS caldav_task ON _id = cd_task "
+          + "WHERE cd_deleted = 0")
+  List<CaldavTaskContainer> getTasks();
+
   @Query("SELECT * FROM caldav_lists ORDER BY cdl_name COLLATE NOCASE")
   List<CaldavCalendar> getCalendars();
 
@@ -97,4 +103,11 @@ public interface CaldavDao {
           + " GROUP BY caldav_lists.cdl_uuid"
           + " ORDER BY caldav_accounts.cda_name COLLATE NOCASE, caldav_lists.cdl_name COLLATE NOCASE")
   List<CaldavFilters> getCaldavFilters(long now);
+
+  @Query(
+      "SELECT tasks._id FROM tasks "
+          + "INNER JOIN tags ON tags.task = tasks._id "
+          + "INNER JOIN caldav_tasks ON cd_task = tasks._id "
+          + "GROUP BY tasks._id")
+  List<Long> getTasksWithTags();
 }
diff --git a/app/src/main/java/org/tasks/data/CaldavTaskContainer.java b/app/src/main/java/org/tasks/data/CaldavTaskContainer.java
new file mode 100644
index 000000000..eb6d8be79
--- /dev/null
+++ b/app/src/main/java/org/tasks/data/CaldavTaskContainer.java
@@ -0,0 +1,9 @@
+package org.tasks.data;
+
+import androidx.room.Embedded;
+import com.todoroo.astrid.data.Task;
+
+public class CaldavTaskContainer {
+  @Embedded public Task task;
+  @Embedded public CaldavTask caldavTask;
+}
diff --git a/app/src/main/java/org/tasks/data/Tag.java b/app/src/main/java/org/tasks/data/Tag.java
index c7e6ba807..4bdb064ae 100644
--- a/app/src/main/java/org/tasks/data/Tag.java
+++ b/app/src/main/java/org/tasks/data/Tag.java
@@ -45,8 +45,13 @@ public class Tag {
 
   @Ignore
   public Tag(Task task, String name, String tagUid) {
-    this.task = task.getId();
-    this.taskUid = task.getUuid();
+    this(task.getId(), task.getUuid(), name, tagUid);
+  }
+
+  @Ignore
+  public Tag(long taskId, String taskUid, String name, String tagUid) {
+    this.task = taskId;
+    this.taskUid = taskUid;
     this.name = name;
     this.tagUid = tagUid;
   }
diff --git a/app/src/main/java/org/tasks/data/TagDao.java b/app/src/main/java/org/tasks/data/TagDao.java
index ad0666921..44769756c 100644
--- a/app/src/main/java/org/tasks/data/TagDao.java
+++ b/app/src/main/java/org/tasks/data/TagDao.java
@@ -1,40 +1,67 @@
 package org.tasks.data;
 
+import static com.google.common.collect.Iterables.transform;
+import static com.google.common.collect.Lists.newArrayList;
+import static com.google.common.collect.Sets.difference;
+import static com.google.common.collect.Sets.newHashSet;
+
 import androidx.room.Dao;
 import androidx.room.Insert;
 import androidx.room.Query;
+import androidx.room.Transaction;
+import com.todoroo.astrid.data.Task;
+import java.util.Collection;
 import java.util.List;
+import java.util.Set;
 
 @Dao
-public interface TagDao {
+public abstract class TagDao {
 
   @Query("UPDATE tags SET name = :name WHERE tag_uid = :tagUid")
-  void rename(String tagUid, String name);
+  public abstract void rename(String tagUid, String name);
 
   @Query("DELETE FROM tags WHERE tag_uid = :tagUid")
-  void deleteTag(String tagUid);
+  public abstract void deleteTag(String tagUid);
 
   @Insert
-  void insert(Tag tag);
+  public abstract void insert(Tag tag);
 
   @Insert
-  void insert(Iterable<Tag> tags);
+  public abstract void insert(Iterable<Tag> tags);
 
   @Query("DELETE FROM tags WHERE task = :taskId AND tag_uid in (:tagUids)")
-  void deleteTags(long taskId, List<String> tagUids);
+  public abstract void deleteTags(long taskId, List<String> tagUids);
 
   @Query("SELECT name FROM tags WHERE task = :taskId ORDER BY UPPER(name) ASC")
-  List<String> getTagNames(long taskId);
+  public abstract List<String> getTagNames(long taskId);
 
   @Query("SELECT * FROM tags WHERE tag_uid = :tagUid")
-  List<Tag> getByTagUid(String tagUid);
+  public abstract List<Tag> getByTagUid(String tagUid);
 
   @Query("SELECT * FROM tags WHERE task = :taskId")
-  List<Tag> getTagsForTask(long taskId);
+  public abstract List<Tag> getTagsForTask(long taskId);
 
   @Query("SELECT * FROM tags WHERE task = :taskId AND tag_uid = :tagUid")
-  Tag getTagByTaskAndTagUid(long taskId, String tagUid);
+  public abstract Tag getTagByTaskAndTagUid(long taskId, String tagUid);
 
   @Query("DELETE FROM tags WHERE _id = :id")
-  void deleteById(long id);
+  public abstract void deleteById(long id);
+
+  @Transaction
+  public boolean applyTags(Task task, TagDataDao tagDataDao,List<TagData> current) {
+    long taskId = task.getId();
+    Set<TagData> existing = newHashSet(tagDataDao.getTagDataForTask(taskId));
+    Set<TagData> selected = newHashSet(current);
+    Set<TagData> added = difference(selected, existing);
+    Set<TagData> removed = difference(existing, selected);
+    deleteTags(taskId, newArrayList(transform(removed, TagData::getRemoteId)));
+    insert(task, added);
+    return !(removed.isEmpty() && added.isEmpty());
+  }
+
+  public void insert(Task task, Collection<TagData> tags) {
+    if (!tags.isEmpty()) {
+      insert(transform(tags, td -> new Tag(task, td)));
+    }
+  }
 }
diff --git a/app/src/main/java/org/tasks/db/DbUtils.java b/app/src/main/java/org/tasks/db/DbUtils.java
new file mode 100644
index 000000000..825cfa37b
--- /dev/null
+++ b/app/src/main/java/org/tasks/db/DbUtils.java
@@ -0,0 +1,28 @@
+package org.tasks.db;
+
+import static com.google.common.collect.Lists.partition;
+
+import java.util.List;
+import org.tasks.Callback;
+
+public class DbUtils {
+
+  private static final int MAX_SQLITE_ARGS = 999;
+
+  public static <T> void batch(List<T> items, Callback<List<T>> callback) {
+    batch(items, MAX_SQLITE_ARGS, callback);
+  }
+
+  public static <T> void batch(List<T> items, int size, Callback<List<T>> callback) {
+    if (items.isEmpty()) {
+      return;
+    }
+    if (items.size() <= size) {
+      callback.call(items);
+    } else {
+      for (List<T> sublist : partition(items, size)) {
+        callback.call(sublist);
+      }
+    }
+  }
+}