/// <summary>
 /// The date and time value as a string.
 /// </summary>
 /// <returns>The string</returns>
 public override string ToString()
 {
     if (InternalValue != string.Empty)
     {
         return(HPMUtilities.HPMDateTimeToDateTimeString(hpmDateTime));
     }
     else
     {
         return(string.Empty);
     }
 }