First or 404

FirstOr404.cs

using System.Linq;

public static class EnumerableUtils {

    // First item, or throw 404 exception
    public static TSource FirstOr404<TSource>(this IEnumerable<TSource> source)
    {
        try
        {
            return source.First();
        }
        catch (InvalidOperationException e)
        {
            throw new HttpException(404, "Not Found");
        }
    }
}