public static string DisableAddNewDetail(this SalesOrderHeader soh)
 {
     if (!soh.IsInProcess())
     {
         return("Can only add to 'In Process' order");
     }
     return(null);
 }
 public static string DisableRecalculate(this SalesOrderHeader soh) =>
 !soh.IsInProcess() ? "Can only recalculate an 'In Process' order" : null;