Adding null check for invalid recents task list. (Bug 17476926)

                ActivityManager.RECENT_IGNORE_UNAVAILABLE |

                ActivityManager.RECENT_INCLUDE_PROFILES |

                ActivityManager.RECENT_WITH_EXCLUDED, userId);

        // Break early if we can't get a valid set of tasks

        if (tasks == null) {

            return new ArrayList<ActivityManager.RecentTaskInfo>();

        }

        boolean isFirstValidTask = true;

        Iterator<ActivityManager.RecentTaskInfo> iter = tasks.iterator();

        while (iter.hasNext()) {