FirstOrDefault

public static class QueryOverExtensions
{
    public static T FirstOrDefault<T, U>(this IQueryOver<T, U> queryOver)
        where T : class
        where U : class
    {
        return queryOver.Take(1).SingleOrDefault();
    }
}

public class TeamEmployeeRepository : Repository<TeamEmployee>, ITeamEmployeeRepository
{
    public TeamEmployee GetFirstEmployee(string name)
    {
        return GetSession().QueryOver<TeamEmployee>()
            .Where(x => x.Name == name)
            .FirstOrDefault();
    }
}