string reference not set to an instance of a string. code example

Example: string reference not set to an instance of a string.

DateTime dt2 = new DateTime();


    dt = DateTime.ParseExact(YearOfRelease, "dd/MM/yyyy hh:mm:ss", null);

    Year = dt.Year.ToString();


    dt2 = DateTime.ParseExact(RunTime, "dd/MM/yyyy hh:mm:ss", null);
    string hour = dt2.Hour.ToString();
    string min = dt2.Minute.ToString();

    Time = hour + ":" + min;