SIPSorcery.SIP.SIPEventPackage.IsValid C# (CSharp) Method

        public static bool IsValid(string value)
        {
            if (value.IsNullOrBlank())
            {
                return false;
            }
            else if (value.ToLower() == "dialog" || value.ToLower() == "message-summary" ||
                value.ToLower() == "presence" || value.ToLower() == "refer")
            {
                return true;
            }
            else
            {
                return false;
            }
        }