NPE when generating WTP configuration files - sometimes - very strange

When running mvn eclipse:eclipse -Dwtpversion=2.0 on my project, I get a NullPointerException, but only in some directories! E.g. when the project sources lie in d:\epa-trunk, I get the following output:

D:\epa-trunk\web>mvn eclipse:eclipse -Dwtpversion=2.0
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'eclipse'.
[INFO] ------------------------------------------------------------------------
[INFO] Building epa-web
[INFO] task-segment: [eclipse:eclipse]
[INFO] ------------------------------------------------------------------------
[INFO] Preparing eclipse:eclipse
[INFO] [enforcer:enforce

Unknown macro: {execution}

]
[INFO] [eclipse:eclipse]
[INFO] Adding support for WTP version 2.0.
[INFO] Using as WTP server : null
[INFO] Adding default classpath contaigner: org.eclipse.jdt.launching.JRE_CONTAINER
[INFO] Using source status cache: D:\epa-trunk\web\target\mvn-eclipse-cache.properties
[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] null
[INFO] ------------------------------------------------------------------------
[INFO] Trace
java.lang.NullPointerException
at org.apache.maven.plugin.ide.IdeDependency.isSystemScopedOutsideProject(IdeDependency.java:519)
at org.apache.maven.plugin.eclipse.writers.wtp.AbstractWtpResourceWriter.writeWarOrEarResources(AbstractWtpResourceWriter.java:280)
at org.apache.maven.plugin.eclipse.writers.wtp.EclipseWtpComponentWriter.writeModuleTypeComponent(EclipseWtpComponentWriter.java:188)
at org.apache.maven.plugin.eclipse.writers.wtp.EclipseWtpComponentWriter.write(EclipseWtpComponentWriter.java:105)
at org.apache.maven.plugin.eclipse.EclipsePlugin.writeConfiguration(EclipsePlugin.java:945)
at org.apache.maven.plugin.ide.AbstractIdeSupportMojo.execute(AbstractIdeSupportMojo.java:494)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:512)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:482)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:330)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:291)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:142)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:336)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:129)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:287)
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.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: 4 seconds
[INFO] Finished at: Mon Dec 29 15:00:14 CET 2008
[INFO] Final Memory: 19M/35M
[INFO] ------------------------------------------------------------------------

When moving the sources to d:\tmp, the build completes successfully:

D:\epa-trunk\web>cd ..\..

D:\>move epa-trunk tmp

D:\>cd tmp\epa-trunk\web

D:\tmp\epa-trunk\web>mvn eclipse:eclipse -Dwtpversion=2.0
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'eclipse'.
[INFO] ------------------------------------------------------------------------
[INFO] Building epa-web
[INFO] task-segment: [eclipse:eclipse]
[INFO] ------------------------------------------------------------------------
[INFO] Preparing eclipse:eclipse
[INFO] [enforcer:enforce

Unknown macro: {execution}

]
[INFO] [eclipse:eclipse]
[INFO] Adding support for WTP version 2.0.
[INFO] Using as WTP server : null
[INFO] Adding default classpath contaigner: org.eclipse.jdt.launching.JRE_CONTAINER
[INFO] Using source status cache: D:\tmp\epa-trunk\web\target\mvn-eclipse-cache.properties
[INFO] File D:\tmp\epa-trunk\web\.project already exists.
Additional settings will be preserved, run mvn eclipse:clean if you want old settings to be removed.
[INFO] Wrote Eclipse project for "epa-web" to D:\tmp\epa-trunk\web.
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4 seconds
[INFO] Finished at: Mon Dec 29 15:01:52 CET 2008
[INFO] Final Memory: 19M/35M
[INFO] ------------------------------------------------------------------------

Remarks:

• web is the web module of my multi-module-project in epa-trunk
• It's the same for wtpversion=1.5.