Your description is really not very clear. Are you saying that if one of the fields in your TemplateValues object is Nothing or an empty string, you want to replace the template field with "N/A"? If so then I'd say that you have two options:

1. Build that functionality into your TemplateValues class:
vb.net Code:
  1. Public Class TemplateViews
  2.  
  3.     Private _clientName As String
  4.     '...
  5.  
  6.     Public Property ClientName() As String
  7.         Get
  8.             Return If(String.IsNullOrEmpty(Me._clientName), "N/A", Me._clientName)
  9.         End Get
  10.         Set(ByVal value As String)
  11.             Me._clientName = value
  12.         End Set
  13.     End Property
  14.  
  15.     '...
  16.  
  17. End Class
2. Use a similar If statement when calling Replace each time:
vb.net Code:
  1. stringToParse = stringToParse.Replace("[CLIENTNAME]", If(String.IsNullOrEmpty(tv.ClientName), "N/A", tv.ClientName))
The first option would be preferable unless that functionality is not logically part of the TemplateValues class.