check this

Author: razzmatazz

src/CSharpLanguageServer/Handlers/Completion.fs

@@ -79,7 +79,7 @@ module Completion =
             let defaultCo: obj =
                 coType.GetField("Default")
                 |> nonNull "Microsoft.CodeAnalysis.Completion.CompletionOptions.Default"
-                |> _.GetValue()
+                |> _.GetValue(null)
 
             { Object = defaultCo
               CompletionOptionsType = coType }