Why is mapping an object PK breaking ExpressMapper?

Trying to implement a generic repository based on an article by Chris Pratt that uses object as the Id (PK).

All is good, until I tried to .Map()one of these objects with ExpressMapper.

More code below. But essentially, when I try and do this:

var dataModel = postedModel.Map(new ExampleDataModel());

It gives me:

No parameterless constructor defined for this object.

When I change the Id property of ExampleDataModel to a string or int it works fine.

I've googled around. I don't see anything obvious, but I am a bit out of my depth. I'd like to know:

• What is causing this?

• Can I work round it somehow?

I'd like to continue using the object PK and ExpressMapper if possible because they're both suiting my project just fine.

public interface IDataModel
{
    object Id { get; }  
}

public interface IDataModel<PKT> : IDataModel
{
    new PKT Id { get; set; }
}

public abstract class DataModel<PKT> : IDataModel<PKT>
{
    public PKT Id { get; set; }
    object IDataModel.Id
    {
        get { return this.Id; }
    }
}



public class ExampleDataModel : 
    DataModel<string>, 
    IDataModel<string>
{
     public virtual string SomeProperty{ get; set; }

    // etc.
}