when building a single module the following exception is thrown
when building the complete project (from the root) no exception is thrown.

...
[INFO] Cobertura Report generation was successful.
[INFO] Generating "Project License" report.
[INFO] Generating "Source Xref" report.
log4j:WARN No appenders could be found for logger (org.apache.commons.digester.Digester.sax).
log4j:WARN Please initialize the log4j system properly.
[PMD] Successfully parsed file /var/hudson/workspace/Security/core/target/pmd.xml of module Security core implementation with 403 warnings.
[CHECKSTYLE] Successfully parsed file /var/hudson/workspace/Security/core/target/checkstyle-result.xml of module Security core implementation with 1525 warnings.
[HUDSON] Archiving /var/hudson/workspace/Security/core/pom.xml to /var/lib/hudson/jobs/Security/modules/it.bz.prov.egov.factory.security$core/builds/2010-09-24_10-28-48/archive/it.bz.prov.egov.factory.security/core/4.0.4-SNAPSHOT/pom.xml
[HUDSON] Archiving /var/hudson/workspace/Security/core/target/core-4.0.4-SNAPSHOT.jar to /var/lib/hudson/jobs/Security/modules/it.bz.prov.egov.factory.security$core/builds/2010-09-24_10-28-48/archive/it.bz.prov.egov.factory.security/core/4.0.4-20100924.082930-2/core-4.0.4-SNAPSHOT.jar
[HUDSON] Archiving /var/hudson/workspace/Security/core/target/core-4.0.4-SNAPSHOT-sources.jar to /var/lib/hudson/jobs/Security/modules/it.bz.prov.egov.factory.security$core/builds/2010-09-24_10-28-48/archive/it.bz.prov.egov.factory.security/core/4.0.4-20100924.082930-2/core-4.0.4-SNAPSHOT-sources.jar
[HUDSON] Archiving /var/hudson/workspace/Security/core/target/core-4.0.4-SNAPSHOT-tests.jar to /var/lib/hudson/jobs/Security/modules/it.bz.prov.egov.factory.security$core/builds/2010-09-24_10-28-48/archive/it.bz.prov.egov.factory.security/core/4.0.4-20100924.082930-2/core-4.0.4-SNAPSHOT-tests.jar
[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] null
[INFO] ------------------------------------------------------------------------
[INFO] Trace
java.lang.NullPointerException
at hudson.maven.reporters.MavenSiteArchiver$1.call(MavenSiteArchiver.java:109)
at hudson.maven.reporters.MavenSiteArchiver$1.call(MavenSiteArchiver.java:106)
at hudson.maven.MavenBuild$ProxyImpl.execute(MavenBuild.java:341)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.perform(RemoteInvocationHandler.java:274)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:255)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:215)
at hudson.remoting.UserRequest.perform(UserRequest.java:114)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:270)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)