[@defaut <value>] seems broken

[toots]

Test:

type foo = {
  bar : string;
  foo : (int [@default 123]);
} [@@deriving yojson]

let () =
  try
    ignore(foo_of_yojson (Yojson.Safe.from_string {|{"bar":"baz"}|}))
  with
    | Ppx_yojson_conv_lib.Yojson_conv.Of_yojson_error (exn, _) ->
        Printf.printf "Error: %s\n%!" (Printexc.to_string exn);
        exit 1

Result:

Error: Failure("test.ml.foo_of_yojson: the following record elements were undefined: foo")