用自定义标签报空指针异常

用自定义标签报空指针异常：求高手指点：
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE taglib
        PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
        "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.0</jsp-version>
<short-name>pageTag</short-name>
<uri>http://org.web.ssh</uri> <tag>
<name>page</name>
<tag-class>com.util.PageTag</tag-class>
<body-content>tagdependent</body-content>
<attribute>
<name>page</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>com.util.PageUtil</type>
</attribute>
</tag></taglib>
jsp页面:<pageTag:page page="${page}"/>
web.xml配置:<!-- 自定义标签配置 -->
<jsp-config>
<taglib>
<taglib-uri>http://org.web.ssh.pageTag</taglib-uri>
<taglib-location>/WEB-INF/tlds/pageTag.tld</taglib-location>
</taglib>
</jsp-config>