Convert to DateTimeOffset from Json Date(Unix epoch)

gistfile1.cs

/// <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;

    var match = Regex.Match(jsondate, @"^\/date\((\d*)([\+\-]?\d*)\)\/+$", RegexOptions.IgnoreCase);

    if (!match.Success) throw new ArgumentException("No match.");

    var ticks = Int64.Parse(match.Groups[1].Value);
    var stroffset = match.Groups[2].Value;

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

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