AutoMapperBug.cs

public class ViewModel
{
    public Guid Id { get; set; }
    public Status? Status { get; set; }
}

public class Model
{
    public Guid Id { get; set; }
    public Status Status { get; set; }
}

public enum Status
{
    Pending,
    Processing,
    Completed
}

private static void Initialize()
{
    Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<ViewModel, Model>()
          .ForAllMembers(o => o.Condition((source, destination, member) => member != null));
    });
}

public static void MergeObject(ViewModel source, Model destination)
{
    Mapper.Map(source, destination);
}