MessageIssueException: Lists must not contain null references right after installing the extension and trying to edit/load/show examples

[chrivo]

Right after installing the extension and trying the first steps (this example: https://github.com/ContextMapper/context-mapper-examples/blob/master/src/main/cml/insurance-example/Insurance-Example-Stage-1.cml) , I get the error below.

I tried downgrading JRE to from

openjdk version "21.0.6" 2025-01-21 LTS OpenJDK Runtime Environment Temurin-21.0.6+7 (build 21.0.6+7-LTS) OpenJDK 64-Bit Server VM Temurin-21.0.6+7 (build 21.0.6+7-LTS, mixed mode, sharing)

...to

openjdk version "17.0.2" 2022-01-18 OpenJDK Runtime Environment Temurin-17.0.2+8 (build 17.0.2+8) OpenJDK 64-Bit Server VM Temurin-17.0.2+8 (build 17.0.2+8, mixed mode, sharing)

...but that didn't help. The same error appears.

Here is the error message:

Juli 02, 2025 8:57:12 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation WARNUNG: Unmatched cancel notification for request id 3 Juli 02, 2025 8:57:14 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError SCHWERWIEGEND: Internal error: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

[Error - 8:57:14 AM] Request textDocument/codeAction failed. Message: Internal error. Code: -32603 java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

Juli 02, 2025 8:57:41 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError SCHWERWIEGEND: Internal error: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

[Error - 8:57:41 AM] Request textDocument/codeAction failed. Message: Internal error. Code: -32603 java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

Juli 02, 2025 8:57:44 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError SCHWERWIEGEND: Internal error: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

[Error - 8:57:44 AM] Request textDocument/codeAction failed. Message: Internal error. Code: -32603 java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

Juli 02, 2025 8:57:45 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError SCHWERWIEGEND: Internal error: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

[Error - 8:57:45 AM] Request textDocument/codeAction failed. Message: Internal error. Code: -32603 java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source) at java.base/java.util.concurrent.CompletableFuture.complete(Unknown Source) at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65) at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1] at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66) at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281) ... 10 more

[stefan-ka]

Hi @chrivo

Hmmm, never saw that one before :-/ On which OS are you? And which Context Mapper version is installed? Does it just happen once and the editor and generators, etc. still work? Or does the language server completely crash after that?

Best regards, Stefan

[chrivo]

Hi Stefan,

I'm on Windows 11. Context Mapper version is the one that the VS Code extension would install today (6.12.0). It happens every time I edit the cml file in VS code, repeatedly. So I would say, the server doesn't crash.

Best regards

• chrivo

[stefan-ka]

@chrivo , alright, I'll have to check whether I can reproduce this. I'll keep you posted.

In the meantime, if you want to try Context Mapper, you may just use it in the browser via Gitpod: https://gitpod.io/#https://github.com/ContextMapper/context-mapper-examples

Best regards, Stefan

[VladimirCascarade]

I have the same error, using JDK 8 on Win11.

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by com.google.common.util.concurrent.AbstractFuture$UnsafeAtomicHelper (file:/C:/[snip]/.vscode/extensions/contextmapper.context-mapper-vscode-extension-6.11.1/lsp/lib/guava-32.1.2-jre.jar)
WARNING: Please consider reporting this to the maintainers of class com.google.common.util.concurrent.AbstractFuture$UnsafeAtomicHelper
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
Oct 23, 2025 4:19:03 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint fallbackResponseError
SEVERE: Internal error: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1]
Lists must not contain null references. Path: $.result[0].arguments[2]
Lists must not contain null references. Path: $.result[1].arguments[1]
Lists must not contain null references. Path: $.result[1].arguments[2]
java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1]
Lists must not contain null references. Path: $.result[0].arguments[2]
Lists must not contain null references. Path: $.result[1].arguments[1]
Lists must not contain null references. Path: $.result[1].arguments[2]
	at java.base/java.util.concurrent.CompletableFuture.wrapInCompletionException(CompletableFuture.java:323)
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:359)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:364)
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:743)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2206)
	at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65)
	at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1]
Lists must not contain null references. Path: $.result[0].arguments[2]
Lists must not contain null references. Path: $.result[1].arguments[1]
Lists must not contain null references. Path: $.result[1].arguments[2]
	at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281)
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:739)
	... 9 more

[Error - 4:19:03 PM] Request textDocument/codeAction failed.
  Message: Internal error.
  Code: -32603 
java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1]
Lists must not contain null references. Path: $.result[0].arguments[2]
Lists must not contain null references. Path: $.result[1].arguments[1]
Lists must not contain null references. Path: $.result[1].arguments[2]
	at java.base/java.util.concurrent.CompletableFuture.wrapInCompletionException(CompletableFuture.java:323)
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:359)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:364)
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:743)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2206)
	at org.eclipse.xtext.ide.server.concurrent.AbstractRequest.complete(AbstractRequest.java:65)
	at org.eclipse.xtext.ide.server.concurrent.ReadRequest.lambda$1(ReadRequest.java:67)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: org.eclipse.lsp4j.jsonrpc.MessageIssueException: Lists must not contain null references. Path: $.result[0].arguments[1]
Lists must not contain null references. Path: $.result[0].arguments[2]
Lists must not contain null references. Path: $.result[1].arguments[1]
Lists must not contain null references. Path: $.result[1].arguments[2]
	at org.eclipse.lsp4j.jsonrpc.validation.ReflectiveMessageValidator.consume(ReflectiveMessageValidator.java:66)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$handleRequest$1(RemoteEndpoint.java:281)
	at java.base/java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:739)
	... 9 more

[stefan-ka]

Hi @VladimirCascarade JDK 8 is no longer supported anyway. You need at least JDK 11, but would recommend >= 17. Best regards, Stefan

[VladimirCascarade]

I have JDK 8, 17.02 and 25.01 installed. I keep getting the same error.