Umbraco Contour Prevalue Source Type for the tags prop editor

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using umbraco.cms.businesslogic.Tags;
using Umbraco.Forms.Core;
using Umbraco.Web;

namespace Contour.Addon.Tags
{
    public class TagsPrevalueSourceType : FieldPreValueSourceType 
    {
        [Umbraco.Forms.Core.Attributes.Setting("TagGroup",
           description = "If you want to limit the tags by a specific group")]
        public string TagGroup { get; set; }

        public TagsPrevalueSourceType()
        {
            this.Id = new Guid("fa2b5315-d1e5-47a4-b6c0-3bc25c860c55");
            this.Name = "List tags";
            this.Description = "Uses the tags datatype as source";
        }


        public override List<PreValue> GetPreValues(Field field)
        {
            var l = new List<PreValue>();

            var tags = new IEnumerable<Tag>();
            if (string.IsNullOrEmpty(TagGroup))
                tags = Tag.GetTags();
            else
                tags = Tag.GetTags(TagGroup);

            int sort = 0;

            foreach(var tag in tags)
            {
                PreValue pv = new PreValue();
                pv.Id = tag.Id;
                pv.Value = tag.TagCaption;
                if (field != null)
                {
                    pv.Field = field.Id;
                }
                pv.SortOrder = sort;
                sort++;
                rl.Add(pv);
            }

            return l;
            
        }

        public override List<Exception> ValidateSettings()
        {
            return new List<Exception>();
        }
    }
}