Inicializa la varible, independiente del tipo de dato. Es decir,
' Declare
Dim oText As String
Dim oNumber As Integer
Dim oCheck As Boolean
oText = Nothing ' Asign NULL
oNumber = Nothing ' Asign 0
oCheck = Nothing ' Asign FALSE
:https://docs.microsoft.com/en-us/dotnet/visual-basic/language-reference/nothing