ResolveUsing ignores Condition issue (AutoMapper 5.2.0)

using AutoMapper;

using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication1
{
    public class Program
    {
        static void Main(string[] args)
        {
            Mapper.Initialize(x =>
            {
                x.AddProfile<ThingProfile>();
            });

            Mapper.AssertConfigurationIsValid();

            var dto1 = new ThingDto();
            dto1.Items = "1,2";
            var dto2 = new ThingDto();

            var thing1 = Mapper.Map<Thing>(dto1);
            var thing2 = Mapper.Map<Thing>(dto2); //Exception here, null reference in resolver.
        }
    }

    public class Thing
    {
        public List<string> Items
        {
            get;
            set;
        }
    }

    public class ThingDto
    {
        public string Items
        {
            get;
            set;
        }
    }

    public class Resolver : IMemberValueResolver<object, object, string, List<string>>
    {
        public List<string> Resolve(object source,
            object destination,
            string sourceMember,
            List<string> destMember,
            ResolutionContext context)
        {
            return sourceMember.Split(',').ToList();
        }
    }

    public class ThingProfile : Profile
    {
        public ThingProfile()
        {
            CreateMap<ThingDto, Thing>()
                .ForMember(dest => dest.Items, conf =>
                {
                    conf.Condition(src => !string.IsNullOrEmpty(src.Items));
                    conf.ResolveUsing<Resolver, string>(source => source.Items);
                });
        }
    }
}