When checking if a string is zero-length, it is better practice, and more efficient, to inspect the length of the string rather than comparing the string to an empty string.
Const myString As String = vbNullString
'Prefer this method when checking if myString is a zero-length string
If Len(myString) = 0 Then
Debug.Print "myString is zero-length"
End If
'Avoid using this method when checking if myString is a zero-length string
If myString = vbNullString Then
Debug.Print "myString is zero-length"
End If