"Cancel" (in generic Excel dialogue box) throws VBA error

Experts:

I need some assistance with and IF/ELSE statement that's executed when pressing either "Ok" or "Cancel" on a standard Excel pop-up form.

Once you open the attached XLSM, do the following:

1. Click on command button "Save and Email".
2. Now, everything works great if I enter a value into the dialogue box and click "Ok".
3. However, if I click on the "Save and Email" and -- for whatever reason -- click "Cancel", I get a VBA error.

How can I modify the existing VBA so that I either a) don't get the error or b) "do nothing" and not get error either? That is, if I click "Cancel", I simply should be returned to the worksheet.

Thank you,
Tom