' FB 1.05.0 Win64

Sub IsEmpty(s As String)
   If Len(s) = 0 Then
     Print "String is empty"
   Else
     Print "String is not empty"
   End If
End Sub

Dim s As String  ' implicitly assigned an empty string
IsEmpty(s)
Dim t As String = "" ' explicitly assigned an empty string
IsEmpty(t)
Dim u As String = "not empty"
IsEmpty(u)
Sleep