gistfile1.txt

   siloBuilder.AddIncomingGrainCallFilter<NotFoundOperationResultInterceptor>();

   [NotFoundIfNotExists(nameof(CreateOrUpdate))]
   public class MyGrain : Grain<MyState>, IMyGrain
   {
      public Task<OperationResult> CreateOrUpdate(MyData data)
      {
      }
   }

    [AttributeUsage(AttributeTargets.Class, Inherited = false)]
    public sealed class NotFoundIfNotExistsAttribute : Attribute
    {
        public NotFoundIfNotExistsAttribute(params string[] ignoreMethods) =>
            IgnoreMethods = new HashSet<string>(ignoreMethods);

        public HashSet<string> IgnoreMethods { get; set; }
    }

    public class NotFoundOperationResultInterceptor : IIncomingGrainCallFilter
    {
        public async Task Invoke(IIncomingGrainCallContext context)
        {
            if (context.Grain is IExistableState grain)
            {
                var type = context.Grain.GetType();
                var attr = type.GetCustomAttribute<NotFoundIfNotExistsAttribute>();
                if (attr != null && !attr.IgnoreMethods.Contains(context.InterfaceMethod.Name))
                {
                    if (!await grain.StateExists())
                    {
                        var argArray = context.InterfaceMethod.ReturnType.GetGenericArguments();
                        var opType = argArray.Any() ? argArray[0] : typeof(object);
                        if (Activator.CreateInstance(opType) is OperationResult opResult)
                        {
                            opResult.Error = new NotFoundError<Guid>
                            {
                                Id = context.Grain.KeyToString(),
                                Type = type.Name
                            };

                            context.Result = opResult;
                            return;
                        }
                    }
                }
            }

            await context.Invoke();
        }
    }