Issue 5989 - Migration crash after updating to 1.3.0

mobile/android/base/java/org/mozilla/gecko/home/HomeConfigPrefsBackend.java

 /* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 package org.mozilla.gecko.home;
 
 import static org.mozilla.gecko.home.HomeConfig.createBuiltinPanelConfig;
 
 import java.util.ArrayList;
@@ skipping 161 matching lines @@
             } else if (type == PanelType.DEPRECATED_REMOTE_TABS) {
                 syncIndex = i;
                 syncFlags = panelConfig.getFlags();
             } else if (type == PanelType.COMBINED_HISTORY) {
                 // Partial landing of bug 1220928 combined the History and Sync panels of users who didn't
                 // have home panel customizations (including new users), thus they don't this migration.
                 return jsonPanels;
             }
         }
 
+        // Since we removed the sync panel, it's expected to not be present at this point
+        // See https://issues.adblockplus.org/ticket/5989
+        if (syncIndex == -1) {
+            final PanelConfig newPanel = createBuiltinPanelConfig(context, PanelType.COMBINED_HISTORY, historyFlags);
+            jsonPanels.put(historyIndex, newPanel.toJSON());
+            return jsonPanels;
+        }
+
         if (historyIndex == -1 || syncIndex == -1) {
             throw new IllegalArgumentException("Expected both History and Sync panels to be present prior to Combined History.");
         }
 
         PanelConfig newPanel;
         int replaceIndex;
         int removeIndex;
 
         if (historyFlags.contains(PanelConfig.Flags.DISABLED_PANEL) && !syncFlags.contains(PanelConfig.Flags.DISABLED_PANEL)) {
             // Replace the Sync panel if it's visible and the History panel is disabled.
@@ skipping 462 matching lines @@
         lbm.unregisterReceiver(mReloadBroadcastReceiver);
     }
 
     private class ReloadBroadcastReceiver extends BroadcastReceiver {
         @Override
         public void onReceive(Context context, Intent intent) {
             mReloadListener.onReload();
         }
     }
 }