使用AutoMapper如何在映射前验证源值？

public class SourceValueValidator : IValueResolver<Source, Destination, string>
{
    public string Resolve(Source source, Destination destination, string destMember, ResolutionContext context)
    {
        // 执行验证操作，如果源值无效则抛出异常
        if (source.Value == null)
        {
            throw new Exception("源值无效。");
        }

        return source.Value;
    }
}

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<Source, Destination>()
        .ForMember(dest => dest.Value, opt =>
        {
            opt.MapFrom<SourceValueValidator>();
        });
});