C:\dev\projects\xwiki>mvn checkstyle:checkstyle
[INFO] Scanning for projects...
[INFO] Reactor build order:
[INFO]   XWiki Platform - Core - Parent POM
[INFO]   XWiki Platform - Core - XMLRPC Parent POM
[INFO]   XWiki Platform - Core - XMLRPC model
[INFO]   XWiki Platform - Core - XMLRPC client
[INFO]   XWiki Platform - Core - Component
[INFO]   XWiki Platform - Core - Observation
[INFO]   XWiki Platform - Core - URL
[INFO]   XWiki Platform - Core - Containers - Parent POM
[INFO]   XWiki Platform - Core - Containers - API
[INFO]   XWiki Platform - Core - Containers - Servlet
[INFO]   XWiki Platform - Core - Velocity
[INFO]   XWiki Platform - Core - Containers - Daemon
[INFO]   XWiki Platform - Core - Containers - Portlet
[INFO]   XWiki Platform - Core - Core
[INFO]   XWiki Platform - Core - Actions
[INFO]   XWiki Platform - Core - Plexus
[INFO]   XWiki Platform - Plugins - Parent POM
[INFO]   XWiki Platform - Plugins - Skin Extensions
[INFO]   XWiki Platform - Plugins - Adwords
[INFO]   XWiki Platform - Plugins - Alexa
[INFO]   XWiki Platform - Plugins - eXo Platform
[INFO]   XWiki Platform - Plugins - Joda Time
[INFO]   XWiki Platform - Plugins - Scheduler
[INFO]   XWiki Platform - Plugins - Application Manager
[INFO]   XWiki Platform - Plugins - Wiki Manager
[INFO]   XWiki Platform - Plugins - Mail Sender
[INFO]   XWiki Platform - Plugins - WatchList Manager
[INFO]   XWiki Platform - Plugins - Swizzle
[INFO]   XWiki Platform - Plugins - Space Manager
[INFO]   XWiki Platform - Plugins - Lucene search
[INFO]   XWiki Platform - Plugins - Activity Stream
[INFO]   XWiki Platform - Plugins - Invitation Manager
[INFO]   XWiki Platform - Skins - Parent POM
[INFO]   XWiki Platform - Skins - Albatross
[INFO]   XWiki Platform - Skins - Dodo
[INFO]   XWiki Platform - Skins - Finch
[INFO]   XWiki Platform - Skins - Toucan
[INFO]   XWiki Platform - Web - Parent POM
[INFO]   XWiki Platform - Web - GWT API
[INFO]   XWiki Platform - Web - Standard
[INFO]   XWiki Platform - Web - Exo
[INFO]   XWiki Platform - Applications - Parent POM
[INFO]   XWiki Platform - Applications - Selenium
[INFO]   XWiki Platform - Applications - Panels
[INFO]   XWiki Platform - Applications - Application Manager
[INFO]   XWiki Platform - Applications - Wiki Manager
[INFO]   XWiki Platform - Applications - Scheduler
[INFO]   XWiki Platform - Applications - S5
[INFO]   XWiki Platform - Applications - S5 - Wiki
[INFO]   XWiki Platform - Applications - Statistics
[INFO]   XWiki Platform - Applications - WatchList
[INFO]   XWiki Products - Enterprise - Parent POM
[INFO]   XWiki Products - Enterprise - Wiki
[INFO]   XWiki Products - Enterprise - Database - Parent POM
[INFO]   XWiki Products - Enterprise - Database - HSQLDB
[INFO]   XWiki Products - Enterprise - Web
[INFO]   XWiki Products - Enterprise - Distribution - Parent POM
[INFO]   XWiki Products - Enterprise - Distribution - HSQLDB
[INFO]   XWiki Top Level POM
[INFO] Searching repository for plugin with prefix: 'checkstyle'.
[INFO] ------------------------------------------------------------------------
[ERROR] FATAL ERROR
[INFO] ------------------------------------------------------------------------
[INFO] An invalid artifact was detected.

This artifact might be in your project's POM, or it might have been included transitively during the resolution process. Here is the information we do have for this artifact:

    o GroupID:     com.xpn.xwiki.platform.tools
    o ArtifactID:  xwiki-verification-resources
    o Version:     <<< MISSING >>>
    o Type:        jar

[INFO] ------------------------------------------------------------------------
[INFO] Trace
org.apache.maven.artifact.InvalidArtifactRTException: For artifact {com.xpn.xwiki.platform.tools:xwiki-verification-resources:null:jar}: The version cannot be empty.
        at org.apache.maven.artifact.DefaultArtifact.validateIdentity(DefaultArtifact.java:147)
        at org.apache.maven.artifact.DefaultArtifact.<init>(DefaultArtifact.java:122)
        at org.apache.maven.artifact.factory.DefaultArtifactFactory.createArtifact(DefaultArtifactFactory.java:158)
        at org.apache.maven.artifact.factory.DefaultArtifactFactory.createDependencyArtifact(DefaultArtifactFactory.java:70)
        at org.apache.maven.project.artifact.MavenMetadataSource.createArtifacts(MavenMetadataSource.java:334)
        at org.apache.maven.plugin.DefaultPluginManager.addPlugin(DefaultPluginManager.java:343)
        at org.apache.maven.plugin.DefaultPluginManager.verifyVersionedPlugin(DefaultPluginManager.java:208)
        at org.apache.maven.plugin.DefaultPluginManager.verifyPlugin(DefaultPluginManager.java:172)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.verifyPlugin(DefaultLifecycleExecutor.java:1257)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.getMojoDescriptor(DefaultLifecycleExecutor.java:1522)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.segmentTaskListByAggregationNeeds(DefaultLifecycleExecutor.java:386)
        at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:138)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:333)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:126)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:282)
        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: 3 seconds
[INFO] Finished at: Fri May 30 13:19:12 CEST 2008
[INFO] Final Memory: 6M/10M
[INFO] ------------------------------------------------------------------------