Portals; IDE page; Attempting to Paste Template HTML for an unsaved Portal results in an unhandled exception

Clicking the "Paste template HTML and JavaScript" button for a page (e.g., the special 'LANDING' page) on the IDE page of the Portals form resulted in an unhandled exception.

This button now displays the message "You must save this Portal before pasting template HTML." as per the corresponding button on the Portal Page form.