I am indexing pages which have a base class with an IList<string> property like below:

public virtual IList<string> TagCodes

{

   get { return new List<string> { "Shoulder", "Knee", "Video" }; }

}

It gets indexed correctly and looks as following when I do index view:

"TagCodes": [
    "Shoulder",
    "Knee",
    "Video"
  ],

However, when I perform the actual search I am getting the following exception "To deserialize objects the $type property must be set.". I am a bit at loss at what is happening and what I am missing.

_searchClient
.Search<ExpertBaseResourcePageType>()
.Select(p => new SearchResultItem
{
   TagCodes = p.TagCodes
} as ISearchResultItem)
.GetResult();

Below is exception stack trace as well:

   at EPiServer.Find.ProjectionHelper.DeserializeObject(JToken root)
   at EPiServer.Find.ProjectionHelper.AddPartialFields(SearchRequestBody requestBody, SearchHit`1 searchHit, Dictionary`2 args)
   at EPiServer.Find.ProjectionHelper.GetFieldValues(SearchRequestBody requestBody, SearchHit`1 searchHit)
   at EPiServer.Find.ProjectionHelper.GetMappedSearchResultItem[TResult](SearchRequestBody requestBody, SearchHit`1 searchHit)
   at EPiServer.Find.ProjectionHelper.GetMappedResult[TResult](SearchRequestBody requestBody, SearchResults`1 jsonResult)
   at EPiServer.Find.SearchExtensions.GetProjectedResult[TResult](ISearch`1 search, SearchContext context)
   at EPiServer.Find.SearchExtensions.GetResult[TResult](ISearch`1 search)