public override string ToString()
        {
            StringBuilder messageBuilder = new StringBuilder();

            foreach (KeyValuePair <string, string> kvp in this)
            {
                EncodingHelper.AddKeyValueString(messageBuilder, EncodingHelper.UrlEncode(kvp.Key), EncodingHelper.UrlEncode(kvp.Value));
            }

            if (this.ExtraQueryParameter != null)
            {
                messageBuilder.Append('&' + this.ExtraQueryParameter);
            }

            return(messageBuilder.ToString());
        }