Activities of "garmiter"

When I use webapi,It's wrong with ValueFactory. Abp.Web.Api/WebApi/Controllers/AbpApiExplorer.cs.

public new  Collection<ApiDescription> ApiDescriptions
        {
            get
            {
                return _apiDescriptions.Value;//this value is null
            }
        }

" message ":" wrong." , "exceptionMessage" : "ValueFactory try to access the instance of the Value attribute." ,"exceptionType":"System.InvalidOperationException"

Is conflict? Thank you very much for your help!