Raven DB unique constraint inserter

RavenUniqueInserter.cs

public interface IRavenUniqueInserter
{
    void StoreUnique<T, TUnique>(
        IDocumentSession session, T entity,
        Expression<Func<T, TUnique>> keyProperty);
}

public class RavenUniqueInserter : IRavenUniqueInserter
{
    public void StoreUnique<T, TUnique>(IDocumentSession session, T entity, 
                                    Expression<Func<T, TUnique>> keyProperty)
    {
        if (session == null) throw new ArgumentNullException("session");
        if (keyProperty == null) throw new ArgumentNullException("keyProperty");
        if (entity == null) throw new ArgumentNullException("entity");

        var key = keyProperty.Compile().Invoke(entity).ToString();

        var constraint = new UniqueConstraint
                                {
                                    Type = typeof (T).Name,
                                    Key = key
                                };

        DoStore(session, entity, constraint);
    }

    static void DoStore<T>(IDocumentSession session, T entity, 
        UniqueConstraint constraint)
    {
        var previousSetting = session.Advanced.UseOptimisticConcurrency;

        try
        {
            session.Advanced.UseOptimisticConcurrency = true;
            session.Store(constraint,
                            String.Format("UniqueConstraints/{0}/{1}",
                                        constraint.Type, constraint.Key));
            session.Store(entity);
            session.SaveChanges();
        }
        catch (ConcurrencyException)
        {
            // rollback changes so we can keep using the session
            session.Advanced.Evict(entity);
            session.Advanced.Evict(constraint);
            throw;
        }
        finally
        {
            session.Advanced.UseOptimisticConcurrency = previousSetting;
        }
    }
}

UsageExample.cs

using (var session = documentStore.OpenSession())
{
    var person = new Person
                   {
                       EmailAddress = "rdingwall@gmail.com",
                       Name = "Richard Dingwall"
                   };
    try
    {
        new RavenUniqueInserter().StoreUnique(session, person, p => p.EmailAddress);
    }
    catch (ConcurrencyException)
    {
        // email address already in use
        ...
    }
}