NotImplementedException when trying to get document diagnostics

I have the following code where I try to get document diagnostics from the language server and it always gives me a NotImplemented exception when I try to get it.

var report = await client.RequestDocumentDiagnostic(new DocumentDiagnosticParams()
{
    TextDocument = textDocument,
    Identifier = "luau"
});

Console.WriteLine(report);

error:

Unhandled exception. System.NotImplementedException: The method or operation is not implemented.
   at OmniSharp.Extensions.LanguageServer.Protocol.Models.RelatedDocumentDiagnosticReport.Converter.ReadJson(JsonReader reader, Type objectType, RelatedDocumentDiagnosticReport existingValue, Boolean hasExistingValue, JsonSerializer serializer)
   at Newtonsoft.Json.JsonConverter`1.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)
   at Newtonsoft.Json.Linq.JToken.ToObject(Type objectType, JsonSerializer jsonSerializer)
   at Newtonsoft.Json.Linq.JToken.ToObject[T](JsonSerializer jsonSerializer)
   at OmniSharp.Extensions.JsonRpc.ResponseRouter.ResponseRouterReturnsImpl.Returning[TResponse](CancellationToken cancellationToken)
   at OmniSharp.Extensions.LanguageServer.Protocol.Progress.ProgressManager.<>c__DisplayClass26_0`1.<<MakeRequest>b__0>d.MoveNext()

Start at RelatedDocumentDiagnosticReport.Converter.ReadJson, the entry point named in the stack trace, and reproduce the RequestDocumentDiagnostic call shown in the issue. Inspect the diagnostic response handling and compare the received report shape with the expected model; done means document diagnostics deserialize without NotImplementedException.