在IDEA修改了web.xml后，点击浏览器图标就没反应了？

Question

web.xml代码：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0" metadata-complete="true">
    <servlet>
        <servlet-name>registerServlet</servlet-name>
        <servlet-class>servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>registerServlet</servlet-name>
        <url-pattern>/servlet/HelloServlet</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

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