NPE when triggering signature help in class file

[asmodeus812]

Using nvim with jdtls i have recently started to receieve the following error. I have not observed this beforehand. No idea what it is or why its occurring
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java. base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:75)\n\tat org. eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:591)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n" RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java. base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:75)\n\tat org. eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:591)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n" RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java. base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:75)\n\tat org. eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:591)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"

[snjeza]

@asmodeus812 could you attach a sample project reproducing the error?

[asmodeus812]

@snjeza I am really not capable of doing that since the project is propriatary and i am not sure what causes this issue. I will try to revert to an older jdtls and see if the issue persists. Do you have any suggestions ?

[asmodeus812]

I did try to downgrade but the same / similar issue persists. What i noticed is that it occurs when i jump to (with document go to definition) source code outside the project, for example even core java classes such as String, Map etc. Steps to reproduce

The error Below was tested and observed in both wsl and macos

1. Cloned this random repo https://github.com/jenkins-docs/simple-java-maven-app.git
2. Jdtls is configured to start as follows (tried with milestone builds 1.6 & 1.9 as well as snapshot build 1.12 - downloaded by default from lspinstaller)
   
3. Open the app.java file
4. Go to definition of a known symbol/clas (String) for example
5. Observe the following error (the message is printed in echo area in vim)

RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"
E21: Cannot make changes, 'modifiable' is off
RPC[Error] code_name = InternalError, message = "Internal error." data = "java.util.concurrent.CompletionException: java.lang.NullPointerException\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Completable
Future.java:314)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)\n\tat java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:645)\n\tat java.
base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:479)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.t
opLevelExec(ForkJoinPool.java:1020)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)\n\tat java.base/java.util.conc
urrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)\nCaused by: java.lang.NullPointerException\n\tat org.eclipse.jdt.ls.core.internal.handlers.SignatureHelpHandler.signatureHelp(SignatureHelpHandler.java:76)\n\tat org.
eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$8(JDTLanguageServer.java:572)\n\tat org.eclipse.jdt.ls.core.internal.BaseJDTLanguageServer.lambda$0(BaseJDTLanguageServer.java:75)\n\tat java.base/java.util.concurren
t.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)\n\t... 6 more\n"

Used configuration for jdtls

                    trace = {
                        server = "message",
                    },
                    signatureHelp = {
                        enabled = true
                    },
                    referenceCodeLens = {
                        enabled = true
                    },
                    format = {
                        enabled = true,
                        settings = {
                            profile = "GoogleStyle",
                            url = opts.format_file or "https://raw.githubusercontent.com/google/styleguide/gh-pages/eclipse-java-google-style.xml"
                        },
                    },
                    saveActions = {
                        organizeImports = true
                    },
                    completion = {
                        importOrder = {
                            "javax",
                            "java",
                            "com",
                            "org"
                        }
                    },
                    codeGeneration = {
                        tostring = {
                            listArrayContents = true,
                            skipNullValues = true,
                            template = "${object.className}{${member.name()}=${member.value}, ${otherMembers}}",
                        },
                        useBlocks = true,
                        hashCodeEquals = {
                            useInstanceof = true,
                            useJava7Objects = true
                        },
                        generateComments = true,
                        insertLocation = true
                    },
                    autobuild = {
                        enabled = true
                    },
                    progressReports = {
                        enabled = false
                    },
                    eclipse = {
                        downloadSources = true
                    },
                    maven = {
                        downloadSources = true,
                        updateSnapshots = true
                    }
                }

Summoning @mfussenegger for expert opinion as well since he has developed the nvim-jdtls plugin and has much better understadning of what might be going wrong here.

[snjeza]

@asmodeus812 could you try to set

"java.signatureHelp.enabled": false,

[asmodeus812]

@snjeza That seems to work, there is no message being reported when i set it to false. I updated the prev post with my initial config btw. (Forgot to do that even though i intended when i was creating it)

[jdneo]

The code at SignatureHelpHandler.java:75 is:

https://github.com/eclipse/eclipse.jdt.ls/blob/73b64b9eacc1f72227ff034a8e71a84351c5567a/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/SignatureHelpHandler.java#L75

Looks like the param of the request is not set correctly?

[mfussenegger]

Summoning @mfussenegger for expert opinion as well since he has developed the nvim-jdtls plugin and has much better understadning of what might be going wrong here.

nvim-jdtls doesn't do anything special in regards to signature help handling, that's all part of neovim-core (and working as far as I can tell). Maybe you're using some other third party plugin that implemented it incorrectly?

You could increase the log level in neovim to also log the payloads sent to the server. (See :help vim.lsp.set_log_level())

[asmodeus812]

Can this be classified as a bug ? Seems like it breaks jdtls with signature enabled

[jdneo]

Ok, then it makes sense. When signature help is triggered in a class file, unit will be null after:

https://github.com/eclipse/eclipse.jdt.ls/blob/28ef246d678b91eea0cddeab72f5bc38c605399b/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/SignatureHelpHandler.java#L74

Then the NPE throws at unit.getBuffer() in
https://github.com/eclipse/eclipse.jdt.ls/blob/73b64b9eacc1f72227ff034a8e71a84351c5567a/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/SignatureHelpHandler.java#L75

Thanks for providing that information! @asmodeus812

BTW, something off the topic: Is it necessary to trigger the signature help for a GTD request? I think SH should go with completion or triggered manually by users.