我遇到了错误，即
警告：找不到映射到令牌名称令牌的令牌
我不明白，请告诉我为什么会收到此错误以及如何解决该错误。
struts.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>

    <package name="interceptorExecAndWait" extends="struts-default">
        <action name="execAndWaitInterceptor" class="com.interceptor.execandwait.action.ExecuteAndWait">
            <!-- <interceptor-ref name="defaultStack"/>  -->
            <interceptor-ref name="completeStack"/>
                    <interceptor-ref name="execAndWait">    
                                    <param name="delay">1000</param>    
                    </interceptor-ref>  
            <!-- <interceptor-ref name="execAndWait"/> -->
            <result name="success">/welcome.jsp</result>
            <result name = "wait">/wait.jsp </result>
            <result name="error">/error.jsp</result>
        </action>
    </package>
</struts>

ExecuteAndWait.java

public class ExecuteAndWait {

    String username;
    String password;

    public String execute() throws InterruptedException {

        if (username.equals("Admin") && password.equals("user")) {
            System.out.println("ok");
            Thread.sleep(5000);
            return "success";
        } else {
            return "error";
        }
    }

    public String getusername() {
        return username;
    }

    public void setusername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }


}

让我知道我在哪里犯错误
 谢谢：）