/// <summary>
/// Convert to DateTimeOffset from Json Date(Unix epoch) 
/// </summary>
/// <param name="jsondate">ex: "/Date(1324707957994+0900)/"</param>
/// <returns></returns>
public Nullable<DateTimeOffset> ConvertToDateTimeOffsetFromJsonDate(string jsondate)
{
	if (String.IsNullOrEmpty(jsondate)) return null;

	Regex regex = new System.Text.RegularExpressions.Regex(@"^\/date\((\d*)([\+\-]?\d*)\)\/+$");
	MatchCollection matchCol = regex.Matches(jsondate.ToLower());

	if (matchCol.Count == 0) throw new InvalidArgumentException("No match.");

	Int64 ticks = Int64.Parse(matchCol[0].Groups[1].ToString());
	string stroffset = matchCol[0].Groups[2].ToString();

	DateTimeOffset offset;
	DateTimeOffset.TryParseExact(stroffset, "zzz", System.Globalization.DateTimeFormatInfo.InvariantInfo, System.Globalization.DateTimeStyles.None, out offset);

	return new DateTimeOffset(new System.DateTime(1970, 1, 1, 0, 0, 0, 0).AddMilliseconds(ticks).Add(offset.Offset), offset.Offset);
}