Sonar/Squid fails on some projects

On one specific project, sonar squid fails with the following stacktrace :

[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Can not execute Sonar

[INFO] ------------------------------------------------------------------------
[DEBUG] Trace
org.apache.maven.lifecycle.LifecycleExecutionException: Can not execute Sonar
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:583)
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:227)
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)
Caused by: org.apache.maven.plugin.MojoExecutionException: Can not execute Sonar
at org.codehaus.mojo.sonar.Bootstraper.executeMojo(Bootstraper.java:87)
at org.codehaus.mojo.sonar.Bootstraper.start(Bootstraper.java:65)
at org.codehaus.mojo.sonar.SonarMojo.execute(SonarMojo.java:117)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451)
at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:558)
... 16 more
Caused by: java.util.NoSuchElementException
at java.util.TreeMap.key(TreeMap.java:1206)
at java.util.TreeMap.firstKey(TreeMap.java:267)
at java.util.TreeSet.first(TreeSet.java:377)
at org.sonar.squid.entities.Resource.getFirstChild(Resource.java:65)
at org.sonar.plugins.squid.SquidMavenCollector.collectFileMeasures(SquidMavenCollector.java:141)
at org.sonar.plugins.squid.SquidMavenCollector.collect(SquidMavenCollector.java:89)
at org.sonar.mojo.InternalMojo.executeCollectors(InternalMojo.java:294)
at org.sonar.mojo.InternalMojo.processModules(InternalMojo.java:176)
at org.sonar.mojo.InternalMojo.execute(InternalMojo.java:160)
at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:451)
at org.codehaus.mojo.sonar.Bootstraper.executeMojo(Bootstraper.java:82)
... 20 more