Why does our Eclipse 3.6 (Helios) PDE Build fail with a NullPointerException?

Our Eclipse RCP application has a headless PDE Build setup from Eclipse 3.2 that's been working for years. We recently updated both the instance of Eclipse we use to do the headless PDE Build and our target platform to 3.6 (principally to be able to create hyperlinks "into" our application), and the headless PDE Build now fails with:

 ...
 [java] generateFeature:
 [java]
 [java] fetch:
 [java]
 [java] generateFeature:
 [java]
 [java] BUILD FAILED
 [java] C:\Projects\[...]\PDE Build\plugins\org.eclipse.pde.build_3.6.2.R36x_20110203\scripts\productBuild\productBuild.xml:39: The following error occurred while executing this line:
 [java] C:\Projects\[...]\PDE Build\plugins\org.eclipse.pde.build_3.6.2.R36x_20110203\scripts\productBuild\productBuild.xml:69: java.lang.NullPointerException
 [java]
 [java] Total time: 0 seconds
 [java] An error has occurred. See the log file
 [java] C:\Projects\[...a separate area dedicated to making builds...]\workspace\.metadata\.log.

The relevant part of the stack trace in the log file would seem to be:

java.lang.NullPointerException
at org.eclipse.pde.internal.build.BundleHelper.getProvisioningAgent(BundleHelper.java:104)
at org.eclipse.pde.internal.build.AbstractScriptGenerator.getAssociatedRepositories(AbstractScriptGenerator.java:625)
at org.eclipse.pde.internal.build.AbstractScriptGenerator.getSite(AbstractScriptGenerator.java:332)
at org.eclipse.pde.internal.build.FeatureGenerator.createFeature(FeatureGenerator.java:339)
at org.eclipse.pde.internal.build.FeatureGenerator.generate(FeatureGenerator.java:161)
at org.eclipse.pde.internal.build.tasks.FeatureGeneratorTask.run(FeatureGeneratorTask.java:54)
at org.eclipse.pde.internal.build.tasks.FeatureGeneratorTask.execute(FeatureGeneratorTask.java:36)
at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
...

The PDE Build Eclipse instance was c开发者_如何学Created according to this process. We tried to produce as clean a target platform as we could, but (in the absence of clear instructions or early success) resorted to unzipping eclipse-rcp-helios-SR2-win32.zip into a directory then unzipping eclipse-3.6.2-delta-pack.zip on top of it.

How can we restore our PDE Build process to working order?

Perhaps our build.properties is too old (from 3.2's template, probably), or perhaps we constructed our target platform improperly, but thanks to a blog post by Kai Tödter, one of the many potential remedies we tried in desperation was (according to Kai's "Trick 1") deleting everything out of our target platform directory except the plugins and features directories. That at least stopped PDE Build mysteriously choking, and error messages then guided us to the rest of the fixups we had to do. (In our case, those fixups consisted almost entirely of updating a secondary (tests) product definition's list of required plugins by clicking "Add Required Plug-ins" and removing a reference to the org.eclipse.ant.optional.junit4 fragment.)

Indeed, it appears that merely deleting either one of the following lines from the target platform's configuration/config.ini is sufficient to unstick PDE Build:

eclipse.p2.profile=epp.package.rcp

(or)

eclipse.p2.data.area=@config.dir/../p2

...though we have preferred to just strip out everything but plugins and fragments lest there be other magical beings hiding in the target platform that could potentially trip us up.

(We don't understand why deleting one of those lines would placate PDE Build . . . but we're back in business.)