title: sonar maven plugin build error, SonarQube version: null
body: <p>My jenkins builds just started to fail with this message:</p>
  
  <pre><code>[INFO] --- sonar-maven-plugin:2.7:sonar (default-cli) @ cividas-core-web ---
  [INFO] artifact com.ontimize:ontimize-core: checking for updates from central
  [INFO] artifact com.ontimize:ontimize-core: checking for updates from imatia-local
  [INFO] artifact com.ontimize:ontimize-core: checking for updates from snapshots
  [INFO] User cache: /var/lib/jenkins/.sonar/cache
  [INFO] SonarQube version: null
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD FAILURE
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time: 3.773s
  [INFO] Finished at: Thu Oct 22 19:49:04 CEST 2015
  [INFO] Final Memory: 13M/193M
  [INFO] ------------------------------------------------------------------------
  [ERROR] Failed to execute goal org.codehaus.mojo:sonar-maven-plugin:2.7:sonar (default-cli) on project cividas-core-web: null: MojoExecutionException: NullPointerException -&gt; [Help 1]
  org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:sonar-maven-plugin:2.7:sonar (default-cli) on project cividas-core-web: null
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:216)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
      at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
      at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
      at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
      at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
      at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:317)
      at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:152)
      at org.apache.maven.cli.MavenCli.execute(MavenCli.java:555)
      at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
      at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:606)
      at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
      at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
      at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
      at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
  Caused by: org.apache.maven.plugin.MojoExecutionException
      at org.codehaus.mojo.sonar.bootstrap.ExceptionHandling.handle(ExceptionHandling.java:41)
      at org.codehaus.mojo.sonar.bootstrap.RunnerBootstrapper.execute(RunnerBootstrapper.java:107)
      at org.codehaus.mojo.sonar.SonarMojo.execute(SonarMojo.java:141)
      at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:106)
      at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
      ... 19 more
  Caused by: java.lang.NullPointerException
      at org.apache.maven.artifact.versioning.ComparableVersion.parseVersion(ComparableVersion.java:354)
      at org.apache.maven.artifact.versioning.ComparableVersion.&lt;init&gt;(ComparableVersion.java:345)
      at org.apache.maven.artifact.versioning.DefaultArtifactVersion.parseVersion(DefaultArtifactVersion.java:110)
      at org.apache.maven.artifact.versioning.DefaultArtifactVersion.&lt;init&gt;(DefaultArtifactVersion.java:46)
      at org.codehaus.mojo.sonar.bootstrap.RunnerBootstrapper.isVersionPriorTo5Dot2(RunnerBootstrapper.java:192)
      at org.codehaus.mojo.sonar.bootstrap.RunnerBootstrapper.execute(RunnerBootstrapper.java:84)
      ... 22 more
  [ERROR] 
  [ERROR] Re-run Maven using the -X switch to enable full debug logging.
  [ERROR] 
  [ERROR] For more information about the errors and possible solutions, please read the following articles:
  [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
  Sonar analysis completed: FAILURE
  </code></pre>
  
  <p>What is this all about?</p>