NameValueCollectionExtensions

using System.Collections.Specialized;
using System.Linq;
using System.Web;

public static class NameValueCollectionExtensions
{
    public static string ToQueryString(this NameValueCollection nvc)
    {
        return string.Join("&", 
            nvc.AllKeys.Where(key => !string.IsNullOrWhiteSpace(nvc[key]))
                .Select(
                    key => string.Join("&", nvc.GetValues(key).Select(val => string.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(val))))));
    }
}