Has anyone got a good bit of code to turn a string into a given type in a type-safe manner

i.e.

VB Code:
  1. Public Shared Function FromString(Of TReturn)(ByVal stringValue As String) As TReturn

  2.  
  3.         If (String.IsNullOrWhiteSpace(stringValue)) Then

  4.             If GetType(TReturn).IsPrimitive Then

  5.                 'get the default

  6.  
  7.             Else

  8.                 Return Nothing

  9.             End If

  10.         Else

  11.             If GetType(TReturn).IsPrimitive Then

  12.  
  13.  
  14.             Else

  15.  
  16.  
  17.             End If

  18.         End If

  19.  
  20.  
  21.     End Function

Anyone got some good ideas on filling in those blanks?