Error message for xslt

I am doing transformation with XSLT and C2.2. When there's something
wrong with the XSL, I get the following message:

javax.servlet.ServletException: org.apache.cocoon.ProcessingException:
Failed to process pipeline
	at <map:serialize type="xml"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:37:33
	at <map:transform type="saxon"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:31:72
	at <map:generate type="validator"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:29:89
	at <map:match> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:27:68
	at org.apache.cocoon.servlet.RequestProcessor.service(RequestProcessor.java:230)
	at org.apache.cocoon.sitemap.SitemapServlet.service(SitemapServlet.java:84)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
	at org.apache.cocoon.servletservice.ServletServiceContext$PathDispatcher.forward(ServletServiceContext.java:468)
.................
	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
	at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:450)
Caused by: org.apache.cocoon.ProcessingException: Failed to process pipeline
	at <map:serialize type="xml"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:37:33
	at <map:transform type="saxon"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:31:72
	at <map:generate type="validator"> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:29:89
	at <map:match> -
file:///C:/workspace/transformation-pipes/pipelines/contents-filesystem/./src/main/resources/COB-INF/sitemap.xmap:27:68
	at org.apache.cocoon.ProcessingException.throwLocated(ProcessingException.java:143)

....................

	at org.apache.cocoon.servlet.RequestProcessor.service(RequestProcessor.java:169)
	... 38 more
Caused by: java.lang.NullPointerException
	at org.apache.cocoon.transformation.TraxTransformer.endDocument(TraxTransformer.java:566)
	at org.apache.xerces.parsers.AbstractSAXParser.endDocument(Unknown Source)
	at org.apache.xerces.impl.dtd.XMLDTDValidator.endDocument(Unknown Source)
	at org.apache.xerces.impl.XMLDocumentScannerImpl.endEntity(Unknown Source)
	at org.apache.xerces.impl.XMLEntityManager.endEntity(Unknown Source)
	at org.apache.xerces.impl.XMLEntityScanner.load(Unknown Source)
	at org.apache.xerces.impl.XMLEntityScanner.skipSpaces(Unknown Source)
	at org.apache.xerces.impl.XMLDocumentScannerImpl$TrailingMiscDispatcher.dispatch(Unknown
Source)
	at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown
Source)
	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
	at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
	at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
	at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
	at org.apache.cocoon.core.xml.impl.JaxpSAXParser.parse(JaxpSAXParser.java:196)
	at org.apache.cocoon.core.xml.impl.JaxpSAXParser.parse(JaxpSAXParser.java:204)
	at org.apache.cocoon.components.source.util.SourceUtil.parse(SourceUtil.java:297)
	at org.apache.cocoon.generation.FileGenerator.generate(FileGenerator.java:136)
	at ca.cpha.repo.pipelines.sax.MonographGenerator.generate(MonographGenerator.java:27)
	at sun.reflect.GeneratedMethodAccessor55.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.cocoon.core.container.spring.avalon.PoolableProxyHandler.invoke(PoolableProxyHandler.java:71)
	at $Proxy25.generate(Unknown Source)
	at org.apache.cocoon.components.pipeline.impl.AbstractCachingProcessingPipeline.processXMLPipeline(AbstractCachingProcessingPipeline.java:360)
	... 56 more


Nothing tells me anything about the error message from the XSLT. Is
there a way to know what is going on ??

Thank you.