Eclipse NPE on project update

Question

I'm using Eclipse 4.4.1 with the latest gae plugins. When I saved da java file in a project, a NPE was thrown: "Errors occurred during the build. Errors running builder 'Enhancer' on project."

Here's the stack trace:

!STACK 0
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.core.resources".
java.lang.NullPointerException
    at com.google.appengine.eclipse.core.orm.enhancement.AutoEnhancer.hasValidSdk(AutoEnhancer.java:188)
    at com.google.appengine.eclipse.core.orm.enhancement.AutoEnhancer.build(AutoEnhancer.java:126)
    at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:734)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:246)
    at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:299)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:302)
    at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:358)
    at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:381)
    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)

!MESSAGE Errors running builder 'Enhancer' on project ...
!STACK 0
java.lang.NullPointerException
    at com.google.appengine.eclipse.core.orm.enhancement.AutoEnhancer.hasValidSdk(AutoEnhancer.java:188)
    at com.google.appengine.eclipse.core.orm.enhancement.AutoEnhancer.build(AutoEnhancer.java:126)
    at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:734)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:246)
    at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:299)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:302)
    at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:358)
    at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:381)
    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)

Answer 1

What's happening is switching between a non WST or WTP project to a WTP configuration, which means the classic GWT/GAE launchers get clobbered for WTP system.

There is a setting not getting switched off when a configuration switches to the new config.

Workaround fix.

1. Optional: Close all unrelated projects - this helps for drilling.
2. Delete the .settings directory - wipes out the settings
3. Run Maven update - rebuilds the .settings for eclipse

This will soon be fixed.