Enable handling of requests with no parameters.

An example of this is the "shutdown" request. It has no parameters (parameter type is void), and so this was failing with a swallowed exception.

Also, log the exception so if there turn out to be any other edge cases they'll be easier to diagnose.

Author: tintoy

src/Server/LspRequestRouter.cs

@@ -121,10 +121,12 @@ public async Task<ErrorResponse> RouteRequest(IHandlerDescriptor descriptor, Req
                     object @params;
                     try
                     {
-                        @params = request.Params.ToObject(descriptor.Params, _serializer.JsonSerializer);
+                        @params = request.Params?.ToObject(descriptor.Params, _serializer.JsonSerializer);
                     }
-                    catch
+                    catch (Exception cannotDeserializeRequestParams)
                     {
+                        _logger.LogError(new EventId(-32602), cannotDeserializeRequestParams, "Failed to deserialise request parameters.");
+
                         return new InvalidParams(request.Id);
                     }