Errors running builder 'Google WebApp Project Validator'

[Bucky]

I just installed juno and when I launched my gwt/gae project I get the following stack trace:

java.lang.NullPointerException

at com.google.gdt.eclipse.core.MarkerUtilities.createMarker(MarkerUtilities.java:65)

at com.google.gdt.eclipse.core.MarkerUtilities.createQuickFixMarker(MarkerUtilities.java:99)

at com.google.gdt.eclipse.core.validators.WebAppProjectValidator.validateBuildClasspath(WebAppProjectValidator.java:142)

at com.google.gdt.eclipse.core.validators.WebAppProjectValidator.build(WebAppProjectValidator.java:100)

at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:728)

at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)

at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:199)

at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:239)

at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:292)

at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)

at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:295)

at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:351)

at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:374)

at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:143)

at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:241)

at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)