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

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



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

    _apply_changeObj: (changeObj) =>
