我正在运行Java的ScriptEngine类以运行某些代码。运行代码时，我将IntelliJ与maven依赖一起使用

Cannot invoke "javax.script.ScriptEngine.eval(String)" because "this.engine" is null
    at Run.Evaluater.<init>(Evaluater.java:19)

下面的代码行

engine.put("event",event);
engine.put("content",message);

这就是我启动ScriptEngone的方式

    public ScriptEngineManager man = new ScriptEngineManager();
    public ScriptEngine engine = man.getEngineByName("nashorn");