Che fails on hover if Language Server returns Hover object with null contents

[philcolol]

Description

If LS returns Hover with empty list inside contents, everything works fine.
But if it returns null inside contents field, Che fails with exception.
Is this intended behavioour?

OS and version:
OS: Win10
Che: 6.6

Diagnostics:
2018-07-19 09:12:57,168[ool-10-thread-1] [INFO ] [o.e.c.a.l.util.OperationUtil 90] - Exception occurred in request java.util.concurrent.CompletionException: java.lang.NullPointerException at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) at java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:659) at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474) at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1962) at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:632) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$request$1(RemoteEndpoint.java:123) at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:77) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:149) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleResponse(RemoteEndpoint.java:162) at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:84) at org.eclipse.che.api.languageserver.TextDocumentService$6.handleResult(TextDocumentService.java:407) at org.eclipse.che.api.languageserver.TextDocumentService$6.handleResult(TextDocumentService.java:391) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.NullPointerException: null at java.util.ArrayList.addAll(ArrayList.java:581) ... 14 common frames omitted at java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:656) at org.eclipse.che.api.languageserver.util.OperationUtil.lambda$doInParallel$0(OperationUtil.java:82) at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:149)

[ghost]

@philcolol what language server is in question and what would be steps to reproduce? Thank you

[philcolol]

Any language server, that returns Hover with null contents. We reproduced this on our custom LS. I created a simple example of such LS: https://github.com/philcolol/ls-examples
Steps:

1. launch che with LS-example
2. open file
3. hover on any word below line 100

[tsmaeder]

I suspect this has been fixed by updating lsp4j to 5.0