NPE possible in org.eclipse.xtext.resource.containers.StateBasedContainerManager#internalGetContainerHandle

https://github.com/eclipse/xtext/blob/9c7e544166dfcf10790eedeaa5c15dc490cb66fc/org.eclipse.xtext/src/org/eclipse/xtext/resource/containers/StateBasedContainerManager.java#L116C1-L118C3

internalGetContainerHandle assumes desc is always nonNull. I have a case where that isn't true (not certain why - I'm still debugging that). If that assumption is deliberate, I suggest adding a comment documenting the assumption and/or adding a throws statement so users know what to expect. If it isn't deliberate, I suggest adding a null pointer check somewhere.

My particular error comes in the middle of code I modified from Lorenzo Bettini's Xtext/XTend book (2nd Edition) - in the SmallJava examaple. Specifically this code:

      @Inject ResourceDescriptionsProvider rdp
      @Inject IContainer.Manager cm

       ....

	def getVisibleContainers(EObject o) {
		val index = rdp.getResourceDescriptions(o.eResource)
		val rd = index.getResourceDescription(o.eResource.URI)
		cm.getVisibleContainers(rd, index)
	}

Apparently the value of rd is null - thus causing the NPE when it gets into internalGetContainerHandle inside the getVisibleContainers call.

Start in org.eclipse.xtext/src/org/eclipse/xtext/resource/containers/StateBasedContainerManager.java at internalGetContainerHandle and inspect how getVisibleContainers passes its resource description. Reproduce the supplied SmallJava example, where getResourceDescription may return null, and determine the intended null contract. Done means the behavior is documented or safely handled with a regression test for the reported path.