How to avoid "Cancel" with Application.InputBox

Hello,

I am using an Application.InputBox when the workbook is opened to prompt the user to input the their initials. These initials are used in other modules throughout the workbook. I added a While loop to keep prompting the user to enter a valid string which is working, but I still get errors if they click "Cancel" on the InputBox. Is there a way I can either keep the user from clicking "Cancel" or at least continue to prompt them to enter their initials if they do?

Private Sub Workbook_Open()

Enterinitials = Application.InputBox("Please Enter Your Initials", "Welcome", Type:=2)
While Len(Enterinitials) = 0
    Enterinitials = Application.InputBox("Enter Valid Initials", Type:=2)
    Wend
    MsgBox "Thank you " & Enterinitials

End Sub

Thank you!