Inicializar String

(Dim str1 As String = "") es lo mismo que (Dim str1 As String=String.Empty)

(Dim str2 As String=Nothing) es lo mismo que (Dim str2 As String)

Fuente: https://stackoverflow.com/questions/25401202/which-is-the-best-way-to-initialize-a-string-with-null-in-vb-net