             opts.cb?(); return
         @close_on_action()
         t = misc.walltime()
-        @execution_queue.clear()
+        @execution_queue?.clear()
         @clear_action_flags(false)
         async.series([
             (cb) =>



    close: =>
        @execution_queue.close()
        super()

    _apply_changeObj: (changeObj) =>

        @close_on_action()
        @clear_action_flags(true)
        # Empty the execution queue.
        @execution_queue?.clear()
        @process_sage_updates(caller:"kill")
        if opts.restart
            @restart(cb:opts.cb)
