Leaving Checkboxes Blank on Email Form

Hello,

I used the code from the following tutorial:

http://www.kirupa.com/web/php_contact_form3.htm

It works as it is supposed to, but I was wondering if there was a way to have it send an email if NO checkbox is selected? Right now, if I test sending an email without checking a box, I get the error:

Warning: Invalid argument supplied for foreach() in /home/content/r/e/l/reluctant13/html/sendmail.php on line 10

Warning: Cannot modify header information - headers already sent by (output started at /home/content/r/e/l/reluctant13/html/sendmail.php:10) in /home/content/r/e/l/reluctant13/html/sendmail.php on line 16

Bascially I would be using the checkbox to ask if the emailer wanted a reply.

Instead of having two seperate boxes with “yes” and “no” I wanted just one box, where I would try and reply if it were checked.

Thanks!
Daniel