def METHOD_NAME(self, app_name):
    """
    Returns the app manager for app with package == app_name if that app is installed.
    Args:
        app_name (str): The name of another Tethys app whose HandoffManager should be returned. If None then self is returned.
    Returns:
        A HandoffManager object for the app with the name app_name or None if no app with that name is found.
    """  # noqa: E501
    if not app_name:
        return self
    # Get the app
    harvester = tethys_apps.harvester.SingletonHarvester()
    apps = harvester.apps
    for app in apps:
        if app.package == app_name:
            manager = app.get_handoff_manager()
            return manager