FELIX-6817 Find no resources in a closed bundle revision

[sharanggupta]

Fixes FELIX-6817.

The NullPointerException in the report (Content.hasEntry(String) called on a null element of the content path, from BundleRevisionImpl.getResourceLocal) happens when a resource lookup through the class loader of a wiring reaches the revision after a refresh has closed it.

BundleWiringImpl.findClassOrResourceByDelegation() checks that the wiring is not disposed before it calls BundleClassLoader.findResource(), but a concurrent refresh can close the revision in between. close() sets the content to null and drops the content path. getContentPath() then rebuilds the path from the null content: MultiReleaseContent.wrap() swallows the resulting exception and returns null, so the cached path is a list holding null, and every later lookup on that revision fails the same way.

initializeContentPath() now returns an empty content path for a closed revision, so the lookup finds nothing, like getResourcesLocal() already does when there is no content path. The empty path is not cached, because a refresh closes all revisions of the bundle and then reopens the current one with resetContent(), after which the path must be computed again.

Test: ResourceLoadingTest.resourceLoadingFromClosedRevisionFindsNothing keeps the class loader of a bundle's wiring, updates and refreshes the bundle, and then calls findResource() and findResources() on the old class loader, which is the state the race leads to. On master it fails with the NullPointerException from the report; with the change it passes, and mvn clean verify of the framework module passes locally.