While working on a plugin idea, I had created a bunch of stub (field-less) meta boxes for a CPT. Trying to save the post caused:

Notice: Undefined offset: 0 in /var/www/httpdocs/wp-content/plugins/piklist/includes/class-piklist-form.php on line 1037


I found that rearranging the conditions helped short circuit before the offending condition generating the notice was reached. Ex:

if (is_array($meta) && count($meta) == 1 && $meta[0])

… as opposed to…

if (is_array($meta) && $meta[0] && count($meta) == 1)