NPE if .java file contains only comments

If a .java file contains only comments, the JXR plugin fails with the following error.

To reproduce, use the quickstart archetype, edit App.java to contain only comments, and add the jxr plugin in the reporting section of the pom. Sample project attached

$mvn site
...
Unable to processPath C:\temp\jxr-test\src\main\java\net\wsmoak\App.java => c:\temp\jxr-test\target/site/xref\net\wsmoak\App.html
[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] null
[INFO] ------------------------------------------------------------------------
[INFO] Trace
java.lang.NullPointerException
at org.apache.maven.jxr.JavaCodeTransform.getHeader(JavaCodeTransform.java:651)
at org.apache.maven.jxr.JavaCodeTransform.transform(JavaCodeTransform.java:716)
at org.apache.maven.jxr.JavaCodeTransform.transform(JavaCodeTransform.java:787)
at org.apache.maven.jxr.JXR.transform(JXR.java:195)
at org.apache.maven.jxr.JXR.processPath(JXR.java:114)
at org.apache.maven.jxr.JXR.xref(JXR.java:335)
at org.apache.maven.plugin.jxr.AbstractJxrReport.createXref(AbstractJxrReport.java:226)
at org.apache.maven.plugin.jxr.AbstractJxrReport.executeReport(AbstractJxrReport.java:352)
at org.apache.maven.reporting.AbstractMavenReport.generate(AbstractMavenReport.java:101)
at org.apache.maven.plugins.site.ReportDocumentRenderer.renderDocument(ReportDocumentRenderer.java:67)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.renderModule(DefaultSiteRenderer.java:239)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.render(DefaultSiteRenderer.java:115)
at org.apache.maven.plugins.site.SiteMojo.renderLocale(SiteMojo.java:124)
at org.apache.maven.plugins.site.SiteMojo.execute(SiteMojo.java:92)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:420)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:539)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalWithLifecycle(DefaultLifecycleExecutor.java:480)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:459)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:311)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:278)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:143)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:330)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:123)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:272)
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:585)
at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)

at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7 seconds
[INFO] Finished at: Tue Mar 27 20:30:55 MST 2007
[INFO] Final Memory: 14M/26M
[INFO] ------------------------------------------------------------------------