Hello Rob, 

Looking through more of the code it looks like if the record cannot be found and raise_if_not_found is True, this line of code will run: 

raise ValueError('No record found for unique ID %s. It may have been deleted.' % (xmlid))

If no record can be found and raise_if_not_found is False then the function will return None. 

This can be seen here on the Github repository. 

Thanks,