VBA Check If Textbox Is Null then send message

Question

first end second if statments working (combobox and textbox <10 ) but third is not(null value). Why?

Private Sub CommandButton1_Click()
If ComboBox1.ListIndex = -1 Then
MsgBox "bla"
Exit Sub
End If
If CDbl(TextBox1.Text) < 10 Then
    MsgBox "bla!"
Exit Sub
End If
If (TextBox1.Value = Null) Then
    MsgBox "bla!"
End If
Exit Sub

Answer 1

I think there is logical error when ı try to reverse if condition between null and smaller its worked. Here is the correct form;

Private Sub CommandButton1_Click()
If ComboBox1.ListIndex = -1 Then
MsgBox "bla"
Exit Sub
End If
End If
If TextBox1.Text= "" Then
    MsgBox "bla!"
End If
Exit Sub
If CDbl(TextBox1.Text) < 10 Then
    MsgBox "bla!"
Exit Sub