Use Document kind instead of merlin_exn

ocaml-lsp-server/src/custom_requests/req_merlin_call_compatible.ml

@@ -120,9 +120,10 @@ let from_structured_json_exn = function
       raise_invalid_params ~data ~message:"Unexpected params format" ())
 
 let with_pipeline state uri specs raw_args cmd_args f =
-  match Document_store.get_opt state.State.store uri with
-  | Some doc ->
-    let merlin = Document.merlin_exn doc in
+  let doc = Document_store.get state.State.store uri in
+  match Document.kind doc with
+  | `Other -> Fiber.return `Null
+  | `Merlin merlin ->
     let open Fiber.O in
     let* config = Document.Merlin.mconfig merlin in
     let specs = List.map ~f:snd specs in
@@ -136,11 +137,6 @@ let with_pipeline state uri specs raw_args cmd_args f =
         cmd_args
     in
     Document.Merlin.with_configurable_pipeline_exn ~config merlin (f args)
-  | None ->
-    let message =
-      "Document " ^ Uri.to_string uri ^ " wasn't found in the document store"
-    in
-    raise_invalid_params ~message ()
 
 let perform_query action params pipeline =
   let action () = action pipeline params in