Automapper sets an array property to a zero-length array rather than null

I found that this was already reported as an issue, and a new configuration option was added (see this commit). At this time, the option is not in the release available via NuGet, but I was able to figure out a way to handle this until the next version is released:

Mapper.CreateMap<Test, Test>()
    .ForMember(t => t.ByteArray, opt => opt.ResolveUsing(t => t.ByteArray == null ? null : t.ByteArray));

Update:

As of version 2.1.265.0, you can using the AllowNullCollections property:

Mapper.Configuration.AllowNullCollections = true;
Mapper.CreateMap<Test, Test>();