Automapper 未将字典映射到对象

I have a .Net 4.6.1 project using Automapper 9.0.0 and the following simple test code:

private MyObj Update(MyInputModel inputModel)
        {
            Dictionary<string, object> blah = new Dictionary<string, object>();
            blah.Add("TypeId", 29);

            var targetObject = RetrieveObjectFromSession<MyObj>(inputModel.Guid);
            var config = new AutoMapper.MapperConfiguration(cfg => cfg.CreateMap<Dictionary<string, object>, MyObj>());
            var mapper = new AutoMapper.Mapper(config);
            mapper.Map(blah, targetObject);
            return targetObject;
        }

The MyObj object has a property on it called TypeId and I've made sure the casing is correct but Automapper just will not update the targetObject with the passed in Dictionary. As far as I can tell from the Automapper documentation, this should be possible.