build number:2.6.0.v20100513-1121

steps to reproduce:
1. new a library
2. new a report, select library and use it
3. preview report in web viewer

expected result:no exception.

actual result:npe

error log:
org.eclipse.birt.report.service.api.reportserviceexception: error happened while running the report
   at org.eclipse.birt.report.service.reportengineservice.throwdummyexception(reportengineservice.java:1097)
   at org.eclipse.birt.report.service.reportengineservice.runreport(reportengineservice.java:1316)
   at org.eclipse.birt.report.service.birtviewerreportservice.runreport(birtviewerreportservice.java:158)
   at org.eclipse.birt.report.service.actionhandler.birtrunreportactionhandler.__execute(birtrunreportactionhandler.java:81)
   at org.eclipse.birt.report.service.actionhandler.birtgetpageactionhandler.__checkdocumentexists(birtgetpageactionhandler.java:58)
   at org.eclipse.birt.report.service.actionhandler.abstractgetpageactionhandler.prepareparameters(abstractgetpageactionhandler.java:119)
   at org.eclipse.birt.report.service.actionhandler.abstractgetpageactionhandler.__execute(abstractgetpageactionhandler.java:104)
   at org.eclipse.birt.report.service.actionhandler.abstractbaseactionhandler.execute(abstractbaseactionhandler.java:90)
   at org.eclipse.birt.report.soapengine.processor.abstractbasedocumentprocessor.__executeaction(abstractbasedocumentprocessor.java:47)
   at org.eclipse.birt.report.soapengine.processor.abstractbasecomponentprocessor.executeaction(abstractbasecomponentprocessor.java:143)
   at org.eclipse.birt.report.soapengine.processor.birtdocumentprocessor.handlegetpage(birtdocumentprocessor.java:87)
   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 org.eclipse.birt.report.soapengine.processor.abstractbasecomponentprocessor.process(abstractbasecomponentprocessor.java:112)
   at org.eclipse.birt.report.soapengine.endpoint.birtsoapbindingimpl.getupdatedobjects(birtsoapbindingimpl.java:66)
   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 org.apache.axis.providers.java.rpcprovider.invokemethod(rpcprovider.java:397)
   at org.apache.axis.providers.java.rpcprovider.processmessage(rpcprovider.java:186)
   at org.apache.axis.providers.java.javaprovider.invoke(javaprovider.java:323)
   at org.apache.axis.strategies.invocationstrategy.visit(invocationstrategy.java:32)
   at org.apache.axis.simplechain.dovisiting(simplechain.java:118)
   at org.apache.axis.simplechain.invoke(simplechain.java:83)
   at org.apache.axis.handlers.soap.soapservice.invoke(soapservice.java:454)
   at org.apache.axis.server.axisserver.invoke(axisserver.java:281)
   at org.apache.axis.transport.http.axisservlet.dopost(axisservlet.java:699)
   at org.eclipse.birt.report.servlet.birtsoapmessagedispatcherservlet.dopost(birtsoapmessagedispatcherservlet.java:265)
   at javax.servlet.http.httpservlet.service(httpservlet.java:727)
   at org.apache.axis.transport.http.axisservletbase.service(axisservletbase.java:327)
   at javax.servlet.http.httpservlet.service(httpservlet.java:820)
   at org.eclipse.birt.report.servlet.birtsoapmessagedispatcherservlet.service(birtsoapmessagedispatcherservlet.java:122)
   at org.eclipse.equinox.http.registry.internal.servletmanager$servletwrapper.service(servletmanager.java:180)
   at org.eclipse.equinox.http.servlet.internal.servletregistration.service(servletregistration.java:61)
   at org.eclipse.equinox.http.servlet.internal.proxyservlet.processalias(proxyservlet.java:126)
   at org.eclipse.equinox.http.servlet.internal.proxyservlet.service(proxyservlet.java:60)
   at javax.servlet.http.httpservlet.service(httpservlet.java:820)
   at org.eclipse.equinox.http.jetty.internal.httpservermanager$internalhttpserviceservlet.service(httpservermanager.java:318)
   at org.mortbay.jetty.servlet.servletholder.handle(servletholder.java:511)
   at org.mortbay.jetty.servlet.servlethandler.handle(servlethandler.java:390)
   at org.mortbay.jetty.servlet.sessionhandler.handle(sessionhandler.java:182)
   at org.mortbay.jetty.handler.contexthandler.handle(contexthandler.java:765)
   at org.mortbay.jetty.handler.handlerwrapper.handle(handlerwrapper.java:152)
   at org.mortbay.jetty.server.handle(server.java:326)
   at org.mortbay.jetty.httpconnection.handlerequest(httpconnection.java:542)
   at org.mortbay.jetty.httpconnection$requesthandler.content(httpconnection.java:939)
   at org.mortbay.jetty.httpparser.parsenext(httpparser.java:756)
   at org.mortbay.jetty.httpparser.parseavailable(httpparser.java:218)
   at org.mortbay.jetty.httpconnection.handle(httpconnection.java:404)
   at org.mortbay.io.nio.selectchannelendpoint.run(selectchannelendpoint.java:409)
   at org.mortbay.thread.queuedthreadpool$poolthread.run(queuedthreadpool.java:582)
caused by: org.eclipse.birt.report.engine.api.engineexception: error happened while running the report
   at org.eclipse.birt.report.engine.api.impl.runtask.dorun(runtask.java:261)
   at org.eclipse.birt.report.engine.api.impl.runtask.run(runtask.java:85)
   at org.eclipse.birt.report.service.reportengineservice.runreport(reportengineservice.java:1307)
... 52 more
caused by: org.eclipse.birt.report.engine.api.engineexception: failed to save design!
   at org.eclipse.birt.report.engine.api.impl.reportdocumentwriter.savedesign(reportdocumentwriter.java:195)
   at org.eclipse.birt.report.engine.api.impl.runtask.dorun(runtask.java:214)
... 54 more
caused by: java.lang.nullpointerexception
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.newelement(reportdesignserializerimpl.java:2869)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.newelement(reportdesignserializerimpl.java:2833)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.createnewelement(reportdesignserializerimpl.java:1260)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.localize(reportdesignserializerimpl.java:1319)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.visitdesignelement(reportdesignserializerimpl.java:266)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.visitcontentelement(reportdesignserializerimpl.java:2993)
   at org.eclipse.birt.report.model.elements.elementvisitorimpl.visitvariableelement(elementvisitorimpl.java:921)
   at org.eclipse.birt.report.model.elements.variableelement.apply(variableelement.java:55)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.handlecontentelementvalue(reportdesignserializerimpl.java:2269)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.localizepropertyvalues(reportdesignserializerimpl.java:2056)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.localizedesign(reportdesignserializerimpl.java:1394)
   at org.eclipse.birt.report.model.util.reportdesignserializerimpl.visitreportdesign(reportdesignserializerimpl.java:212)
   at org.eclipse.birt.report.model.elements.reportdesign.apply(reportdesign.java:65)
   at org.eclipse.birt.report.model.api.util.documentutil.localizedesign(documentutil.java:90)
   at org.eclipse.birt.report.model.api.util.documentutil.serialize(documentutil.java:67)
   at org.eclipse.birt.report.engine.api.impl.reportdocumentwriter.savedesign(reportdocumentwriter.java:186)
... 55 more
cannot reproduce it.