nvim client compatibility fails with null/empty config data

[awilkins]

Started a basic nvim-lspconfig config (please ignore all my horrible assumptions)

local fs = require('vim.fs')

return {
  default_config = {
    cmd = { 'java', '-jar', fs.abspath('~/vscode/natls/libs/natls/build/libs/natls.jar') },
    filetypes = { 'natural' },
    root_dir = function(dir)
      return fs.root(dir, '.natural')
    end,
  },
  docs = {
    description = [[
https://github.com/MarkusAmshove/vscode-natural

Natural Language Server
]],
  },
}

Sadly on connection it stops on this error

Error executing vim.schedule lua callback: /usr/local/share/nvim/runtime/lua/vim/lsp/client.lua:548: RPC[Error] code_name = InternalError, message = "Internal error." data = 'java.util.concurrent.CompletionException: java.lang.NullPointerException: Cannot invoke "org.amshove.natls.config.InitializationConfiguration.isAsync()" because the return value of "org.amshove.natls.config.LSConfiguration.getInitialization()" is null\n\tat java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315)\n\tat java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320)\n\tat java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1770)\n\tat java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1760)\n\tat java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)\n\tat java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)\n\tat java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)\n\tat java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)\n\tat java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)\nCaused by: java.lang.NullPointerException: Cannot invoke "org.amshove.natls.config.InitializationConfiguration.isAsync()" because the return value of "org.amshove.natls.config.LSConfiguration.getInitialization()" is null\n\tat org.amshove.natls.languageserver.NaturalLanguageService.indexProject(NaturalLanguageService.java:115)\n\tat org.amshove.natls.languageserver.NaturalLanguageServer.lambda$initialize$1(NaturalLanguageServer.java:136)\n\tat java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1768)\n\t... 6 more\n'
stack traceback:
	[C]: in function 'assert'
	/usr/local/share/nvim/runtime/lua/vim/lsp/client.lua:548: in function ''
	vim/_editor.lua: in function <vim/_editor.lua:0>

Not sure which path it's taking to initialize the config. I tried a couple of configs passing a struct to init_options but couldn't manage to set the async property.

A small patch to NaturalLanguageService on line 115 ...

		if (getConfig().getInitialization() != null && !getConfig().getInitialization().isAsync())

... and nvim works (not had a proper play with it yet).

It seems to be generally agreed that starting a server without initialization options should "just work", but I'm not sure this is what's happening ; wondering if nvim's LSP client is supplying an empty string value here.

[MarkusAmshove]

Good find. VSCode sends default configuration and I've had my lsp-config send configuration since the server supported configuration.
I'll leave my configuration here, in case you're wondering how to pass the configuration.
But nonetheless, we should do the null check, because crashing is always bad.

local function register_natural()
  local root_files = { { '.natural', '_naturalBuild' } }

  local my_util = require'dotfiles.util'
  local user_home = my_util.get_user_home()
  local server_path = user_home .. '/dev/natls/libs/natls/build/libs/natls.jar'

  local lspconfig = require 'lspconfig'
  local configs = require 'lspconfig.configs'
  local lsp_util = require 'lspconfig.util'

  local java_path = "/usr/lib64/jvm/jdk-21.0.2+13/bin/java"
  local debugargs =  '-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000'
  -- local debugargs = ""

  if not configs.natls then
    configs.natls = {
      default_config = {
        cmd = {java_path, debugargs, '-jar', server_path },
        filetypes = { 'natural' },
        root_dir = function (fname)
          for _, patterns in ipairs(root_files) do
            local root = lsp_util.root_pattern(unpack(patterns))(fname)
            if root then
              return root
            end
          end
        end,
        single_file_mode = false,
        init_options = {
          completion = {
            qualify = true
          },
        },
      }
    }
  end

  lspconfig.natls.setup {
    on_attach = after_attach
  }
end