sonar maven plugin build error, SonarQube version: null

Question

My jenkins builds just started to fail with this message:

[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 -> [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.<init>(ComparableVersion.java:345)
    at org.apache.maven.artifact.versioning.DefaultArtifactVersion.parseVersion(DefaultArtifactVersion.java:110)
    at org.apache.maven.artifact.versioning.DefaultArtifactVersion.<init>(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

What is this all about?

Answer 1

Solved by downgrading the automatically picked latest (2.7) version to an older one (2.4) by adding this code to the plugins section of my pom.xml

  <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>sonar-maven-plugin</artifactId>
    <version>2.4</version>
  </plugin>