I'm using NHibernate to store downloads in my MySQL database for an ASP.NET MVC website. I am using to classes. One called `Download` for the download itself and one called `DownloadContent` for the file itself (so I can load it easier when I just want to get the metadata).

The data class declarations and mappings look like this:

```
public class Download
{
    public virtual string Id { get; set; }
    public virtual string OutFileName { get; set; }
    public virtual DownloadContent Contents { get; set; }
    public virtual string MimeType { get; set; }
    public virtual bool DoForward { get; set; }
    public virtual string RedirectLink { get; set; }
}

public class DownloadMap : ClassMap<Download>
{
    public DownloadMap()
    {
        Id(x => x.Id);
        Map(x => x.OutFileName);
        References<DownloadContent>(x => x.Contents);
        Map(x => x.MimeType);
        Map(x => x.DoForward).Not.Nullable();
        Map(x => x.RedirectLink);
    }
}

public class DownloadContent
{
    public virtual byte[] Data { get; set; }
}

public class DownloadContentMap : ClassMap<DownloadContent>
{
    public DownloadContentMap()
    {
        Id();
        Map(x => x.Data).CustomType("BinaryBlob");
    }
}

```

Now, when I try to do like this:

```
dl.Contents = new DownloadContent { Data = content };
db.session.SaveOrUpdate(content);

```

I get an `NHibernate.MappingException` with the message "No persister for: System.Byte[]". I looked it up with the NHibernate docs and byte[] should map correctly.

What am I doing wrong?