Why am I getting a "Nullable object must have a value" exception when I'm using Condition?

I'm getting a "Nullable object must have a value" in the example code below. Why do I need the following fix to make this work: ``` .ForMember(dest => dest.ShirtColor, dest => dest.MapFrom(src => src.ShirtColor != null ? new OptionSetValue((int) src.ShirtColor) : null)) ``` ``` AutoMapper.Mapper.CreateMap<PersonA, PersonB>() .ForMember(dest => dest.FirstName, dest => dest.MapFrom(src => src.FirstName)) .ForMember(dest => dest.LastName, dest => dest.MapFrom(src => src.LastName)) // Condition to avoid overwriting existing data!!! .ForMember(dest => dest.ShirtColor, dest => dest.Condition(src => src.ShirtColor != null)) .ForMember(dest => dest.ShirtColor, dest => dest.MapFrom( src => new OptionSetValue((int)src.ShirtColor))) // Fix that should not be needed due to condition: //.ForMember(dest => dest.ShirtColor, // dest => dest.MapFrom( // src => src.ShirtColor != null // ? new OptionSetValue((int) src.ShirtColor) // : null)); PersonA source = new PersonA(); source.FirstName = "Thomas"; source.LastName = "Jefferson"; source.ShirtColor = null; // nullable int PersonB destination = new PersonB(); destination.FirstName = "Thomas"; destination.LastName = "Jefferson"; destination.ShirtColor = new OptionSetValue(4); // Results in: "Nullable object must have a value" despite the fact that // condition should have been met! Mapper.Map<PersonA, PersonB>(source, destination); Debug.Assert(destination.ShirtColor != null); Console.WriteLine("Our existing data was not overwritten!!"); Console.WriteLine("Hit enter to exit"); Console.ReadLine(); ``` Here is how OptionSet is defined: public class OptionSetValue { public OptionSetValue(){} ``` public OptionSetValue(int value) { Number = value; } public int Number { get; set; } } ```