Custom ASPNETCORE Scaffolding extension is throw exception with word Key

I created a custom extension for Asp.net core scaffolding.  I  updated visual studio 2019 16.6 version and then install custom scaffolding extension into visual studio then perform scaffolding in core application it's throw exception with word"Key". Also created extension is worked for visual studio 2019 previous version


Exception:


We used below code for Config scaffolding

 [Export("NetCoreScaffolderFactory", typeof(CodeGeneratorFactory))]
    public class BlazorCodeGeneratorFactoryConfig : BlazorCodeGeneratorFactory, IConfigurableScaffolderFactory
    {

        /// <summary>
        /// evaluate a selected code generation context
        /// </summary>
        /// <param name="factoryEvaluationContext"></param>
        /// <returns></returns>
        public bool IsEvaluationContextInitialized(IScaffolderFactoryConfigEvaluationContext factoryEvaluationContext)
        {
            return true;
        }
        /// <summary>
        /// check selected code generation context is supported for selected project if yes, return true.
        /// </summary>
        /// <param name="facotryEvaluationContext"></param>
        /// <returns></returns>
        public bool IsSupported(IScaffolderFactoryConfigEvaluationContext facotryEvaluationContext)
        {
            return true;

        }

        public IScaffolderFactoryConfigEvaluationContext SetupConfigEvaluationContext(CodeGenerationContext context)
        {
            return null;
        }

    }