Dijt FilteringSelect and EpiServer rest store issues

I have put together a widget which essentialy will allow users to select documents from external system and save links to them.

I have used a dijit FilteringSelect to achieve this together with Epi RestStore but I stumbled upon couple of issues.

1. when there is value already set for the widget, (guid in my example), when dijit is making call to the RestStore, the call is like this: /modules/app/Stores/myreststore/a34f3fd8-8b9b-457f-9cde-56d8b886ff5b, and the value is not binded properly - the id is part of the path, and reststore controller treats it like null so I can't resolve the exact item for the store
2. when I select value from the drop-down, it fails store the value with following error in console:
   

   Uncaught TypeError: Cannot read property 'toString' of undefined
       at Object._announceOption (widgets.js:2)
       at Object._selectOption (widgets.js:2)
       at Object.<anonymous> (dojo.js:15)
       at Object.advice (dojo.js:15)
       at Object._264 [as onChange] (dojo.js:15)
       at Object.onClick (widgets.js:2)
       at Object.<anonymous> (widgets.js:2)
       at dojo.js:15
       at Object.<anonymous> (widgets.js:2)
       at dojo.js:15

Model that I return from rest store:

    internal class Document
    {
        public Guid Id { get; set; }
        public string Title { get; set; }
        public string Author { get; set; }
        public DateTime ModificationDate { get; set; }
    }

Get method for the rest controller:

public RestResult Get(string query)
        {
            var results = Enumerable.Empty<Document>();
            if (string.IsNullOrEmpty(query) || query == "*")
            {
                results = documents;
            }
            else
            {
                query = query.Replace("*", String.Empty).ToLowerInvariant();
                if (Guid.TryParse(query, out var docId))
                {
                    results = documents.Where(doc => doc.Id == docId);
                }
                else
                {
                    results = documents.Where(doc =>
                            doc.Author.ToLowerInvariant().Contains(query) ||                            
                            doc.Title.ToLowerInvariant().Contains(query))
                        .Take(10);
                }
            }
            return Rest(results);
        }

Any help highly appreciated.