Issue 5989 - Migration crash after updating to 1.3.0

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

Index: mobile/android/base/java/org/mozilla/gecko/home/HomeConfigPrefsBackend.java
===================================================================
--- a/mobile/android/base/java/org/mozilla/gecko/home/HomeConfigPrefsBackend.java
+++ b/mobile/android/base/java/org/mozilla/gecko/home/HomeConfigPrefsBackend.java
@@ -174,16 +174,24 @@ public class HomeConfigPrefsBackend impl
                 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;