Null substitution

Null substitution allows you to supply an alternate value for a destination member if the source value is null anywhere along the member chain.

var config = new MapperConfiguration(cfg => cfg.CreateMap<Source, Dest>()
    .ForMember(dest => dest.Value, opt => opt.NullSubstitute("Other Value"));

var source = new Source { Value = null };
var mapper = config.CreateMapper();
var dest = mapper.Map<Source, Dest>(source);

dest.Value.ShouldEqual("Other Value");

source.Value = "Not null";

dest = mapper.Map<Source, Dest>(source);

dest.Value.ShouldEqual("Not null");