This issue appears to have been reported before:

http://www.mail-archive.com/users@maven.apache.org/msg16864.html

Would seem to be due to incorrect class loader. Any temporary workarounds for this issue will be most gratefully received.

Stacktrace for NPE attached.

I have the same problem, I tried to redefine the classpath inside ant task, and the same problem appeared.
Does anyone have idea how to correct this? or any workaround?

Thanks in advance,
Breno Leitão
CPqD IT & Telecom

I found a comment in maven.xml file, it tries to redefine the classpath. See below:

<!-- When invoking ant:ant, ant's task rmic and xslt are broken due to
a null classloader. This will only be fixed in Maven 2.0, so
below is a workaround -->

<goal name="invoke-ant" description="execute ant">
<j:set var="log.name" value="${glassfish.module.name}.log"/>
<ant:delete file="${log.name}" failonerror="false"/>
<j:catch>
<ant:record name="${log.name}" loglevel="verbose" action="start"/>
</j:catch>

<java classname="org.apache.tools.ant.Main" fork="true" failonerror="false" maxmemory="128M">
<classpath>
<fileset dir="${glassfish.home}/lib/ant/lib">
<include name="*.jar" />
</fileset>
<pathelement path="${java.home}/../lib/tools.jar" />
</classpath>
<sysproperty key="ant.home" value="${glassfish.home}/lib/ant" />
<arg line="-f ${module.dir}/build.xml -Dglassfish.home=${glassfish.home} ${ant.target}" />
</java>
</goal>