Fix null pointer exceptions on backup import

app/src/main/java/org/tasks/backup/BackupContainer.java

@@ -20,10 +20,10 @@ import org.tasks.data.UserActivity;
 
 class BackupContainer {
 
-  final List<TaskBackup> tasks;
-  final List<TagData> tags;
-  final List<Filter> filters;
-  final List<GoogleTaskList> googleTaskLists;
+  private final List<TaskBackup> tasks;
+  private final List<TagData> tags;
+  private final List<Filter> filters;
+  private final List<GoogleTaskList> googleTaskLists;
   private final List<GoogleTaskAccount> googleTaskAccounts;
   private final List<CaldavAccount> caldavAccounts;
   private final List<CaldavCalendar> caldavCalendars;
@@ -45,6 +45,22 @@ class BackupContainer {
     this.caldavCalendars = caldavCalendars;
   }
 
+  public List<TaskBackup> getTasks() {
+    return tasks == null ? emptyList() : tasks;
+  }
+
+  public List<TagData> getTags() {
+    return tags == null ? emptyList() : tags;
+  }
+
+  public List<Filter> getFilters() {
+    return filters == null ? emptyList() : filters;
+  }
+
+  public List<GoogleTaskList> getGoogleTaskLists() {
+    return googleTaskLists == null ? emptyList() : googleTaskLists;
+  }
+
   public List<CaldavAccount> getCaldavAccounts() {
     return caldavAccounts == null ? emptyList() : caldavAccounts;
   }

app/src/main/java/org/tasks/backup/TasksJsonImporter.java

@@ -128,7 +128,7 @@ public class TasksJsonImporter {
     try {
       JsonElement data = input.get("data");
       BackupContainer backupContainer = gson.fromJson(data, BackupContainer.class);
-      for (TagData tagData : backupContainer.tags) {
+      for (TagData tagData : backupContainer.getTags()) {
         if (tagDataDao.getByUuid(tagData.getRemoteId()) == null) {
           tagDataDao.createNew(tagData);
         }
@@ -138,12 +138,12 @@ public class TasksJsonImporter {
           googleTaskListDao.insert(googleTaskAccount);
         }
       }
-      for (GoogleTaskList googleTaskList : backupContainer.googleTaskLists) {
+      for (GoogleTaskList googleTaskList : backupContainer.getGoogleTaskLists()) {
         if (googleTaskListDao.getByRemoteId(googleTaskList.getRemoteId()) == null) {
           googleTaskListDao.insert(googleTaskList);
         }
       }
-      for (Filter filter : backupContainer.filters) {
+      for (Filter filter : backupContainer.getFilters()) {
         if (filterDao.getByName(filter.getTitle()) == null) {
           filterDao.insert(filter);
         }
@@ -158,7 +158,7 @@ public class TasksJsonImporter {
           caldavDao.insert(calendar);
         }
       }
-      for (BackupContainer.TaskBackup backup : backupContainer.tasks) {
+      for (BackupContainer.TaskBackup backup : backupContainer.getTasks()) {
         taskCount++;
         setProgressMessage(activity.getString(R.string.import_progress_read, taskCount));
         Task task = backup.task;