RuntimeException when ctrl+hover over external symbol

[iTob191]

In VSCode, hovering over any name in an expression that does not originate in the current resource (e.g. blank in "".blank or a field in an imported model) and pressing ctrl (= go to definition) results in the following exception:

java.util.concurrent.CompletionException: java.lang.RuntimeException: Cannot create a resource for 'java:/Objects/java.lang.String'; a registered resource factory is needed
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:332)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:347)
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:708)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2194)
	at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.logAndCompleteExceptionally(AbstractRequest.java:73)
	at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:69)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
	at java.base/java.lang.Thread.run(Thread.java:1570)
Caused by: java.lang.RuntimeException: Cannot create a resource for 'java:/Objects/java.lang.String'; a registered resource factory is needed
	at org.eclipse.xtext.resource.XtextResourceSet.getResource(XtextResourceSet.java:263)
	at org.eclipse.xtext.ide.server.ProjectManager.getResource(ProjectManager.java:181)
	at org.eclipse.xtext.ide.server.WorkspaceManager.read(WorkspaceManager.java:470)
	at org.eclipse.xtext.ide.server.WorkspaceManager.doRead(WorkspaceManager.java:454)
	at org.eclipse.xtext.ide.server.findReferences.WorkspaceResourceAccess.readOnly(WorkspaceResourceAccess.java:36)
	at org.eclipse.xtext.ide.server.symbol.DocumentSymbolService.doRead(DocumentSymbolService.java:323)
	at org.eclipse.xtext.ide.server.symbol.DocumentSymbolService.getDefinitions(DocumentSymbolService.java:111)
	at org.eclipse.xtext.ide.server.symbol.DocumentSymbolService.getDefinitions(DocumentSymbolService.java:97)
	at org.eclipse.xtext.ide.server.LanguageServerImpl.lambda$28(LanguageServerImpl.java:639)
	at org.eclipse.xtext.ide.server.WorkspaceManager.doRead(WorkspaceManager.java:458)
	at org.eclipse.xtext.ide.server.LanguageServerImpl.definition(LanguageServerImpl.java:638)
	at org.eclipse.xtext.ide.server.LanguageServerImpl.definition(LanguageServerImpl.java:626)
	at org.eclipse.xtext.ide.server.LanguageServerImpl.lambda$27(LanguageServerImpl.java:617)
	at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:66)
	... 5 more

I'm not sure whether this is a bug in Xtext or somehow related to the NeoJoin setup.