Return VOID by default for unhandled requests

lib/ruby_lsp/executor.rb

@@ -178,6 +178,8 @@ def run(request)
         workspace_symbol(request.dig(:params, :query))
       when "rubyLsp/textDocument/showSyntaxTree"
         show_syntax_tree(uri, request.dig(:params, :range))
+      else
+        VOID
       end
     end
 

test/executor_test.rb

@@ -217,6 +217,15 @@ def test_shows_error_if_formatter_set_to_rubocop_but_rubocop_not_available
     end
   end
 
+  def test_returns_void_for_unhandled_request
+    executor = RubyLsp::Executor.new(@store, @message_queue)
+
+    result = executor.execute(method: "anything/not/existing", params: {})
+    assert_same(RubyLsp::VOID, result.response)
+  end
+
+  private
+
   def with_uninstalled_rubocop(&block)
     rubocop_paths = $LOAD_PATH.select { |path| path.include?("gems/rubocop") }
     rubocop_paths.each { |path| $LOAD_PATH.delete(path) }
@@ -237,8 +246,6 @@ def unload_rubocop_runner
     # Depending on which tests have run prior to this one, `RuboCopRunner` may or may not be defined
   end
 
-  private
-
   def stub_dependencies(rubocop:, syntax_tree:)
     dependencies = {}
     dependencies["syntax_tree"] = "..." if syntax_tree