Gremlin.Net: Message with op code [close] is not recognized

Question

I am trying to run this query against AWS Neptune Db using Gremlin .Net client and I getting an exception with message.

Message with op code [close] is not recognized.

Is there something wrong in this code?

var query = graph.V().Values<string>("resourceId").Dedup();
using (var uniqueResourceIds = query.Project<string>("resourceId"))
{
    var queryResult = await uniqueResourceIds.Promise(x => x.ToList());
} // No error while awaiting the response. Getting the error when the execution of code is moving forward from the "using" block.