为什么web.xml错误
<?xml   version= "1.0 "   encoding= "UTF-8 "?>
<web-app   xmlns= "http://java.sun.com/xml/ns/j2ee "   xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance "   version= "2.4 "   xsi:schemaLocation= "http://java.sun.com/xml/ns/j2ee       http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd ">

    <!--   Standard   Action   Servlet   Configuraction   -->
    <servlet>
    <servlet-name> action </servlet-name>
    <servlet-class> org.apache.struts.action.ActionServlet </servlet-class>
   
    <init-param>
  <param-name> config </param-name>  
    <param-value> /WEB-INF/struts-config.xml </param-value>
    </init-param>
    <load-on-startup> 2 </load-on-startup>
    </servlet>
   
    <!--   Standard   Action   Servlet   Mapping   -->
    <servlet-mapping>
    <servlet-name> action </servlet-name>
    <url-pattern> *.do </url-pattern>
    </servlet-mapping>
   
    <!--   The   Usual   Welcome   File   List   -->
    <welcome-file-list>
    <welcome-file> hello.jsp </welcome-file>
    </welcome-file-list>
   
    <!--   Struts   Tag   Library   Descriptors   -->
      <taglib>
    <taglib-url> /WEB-INF/tld/struts-bean.tld </taglib-url>
<taglib-location> /WEB-INF/struts-bean.tld </taglib-location>
      </taglib>
   
    <taglib>
    <taglib-url> /WEB-INF/tld/struts-html.tld </taglib-url>
<taglib-location> /WEB-INF/struts-html.tld </taglib-location>
    </taglib>
   
      <taglib>
    <taglib-url> /WEB-INF/tld/struts-logic.tld </taglib-url>
    <taglib-location> /WEB-INF/struts-logic.tld </taglib-location>
      </taglib>
</web-app>


提示这里错误
      <taglib>
    <taglib-url> /WEB-INF/tld/struts-bean.tld </taglib-url>
<taglib-location> /WEB-INF/struts-bean.tld </taglib-location>
      </taglib>


java.lang.IllegalArgumentException:   Can 't   convert   argument:   null
at   org.apache.tomcat.util.IntrospectionUtils.convert(IntrospectionUtils.java:975)
at   org.apache.tomcat.util.digester.CallMethodRule.end(CallMethodRule.java:522)
at   org.apache.tomcat.util.digester.Rule.end(Rule.java:228)
at   org.apache.tomcat.util.digester.Digester.endElement(Digester.java:1057)
at   com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:633)
at   com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDoc