Cannot Pass null with GraphQL Variable Values

[DimuthuMadushan]

Description:
When GraphQL service resource function has a nullable type input parameter, It should be able to pass null as the input value via variable json. But the service returns a validation error.

Consider the following service:

service on new graphql:Listener(9000) {
    resource function get name(string? name) returns string {
        if name is () {
            return "GraphQL";
        }
        return name;
    }
}

This can be queried using following content:

{
  "query": "query($name:String){ name(name:$name) }",
  "variables": { "name": null }
}

But this returns an error: Variable name expected value of type \"String\", found