Simple custom get custom field function, which handles when a key doesn't exist.

gistfile1.aw

<?php
function template_get_custom_field($custom, $key, $prefix = 'custom_') {
	if(!empty($custom[$prefix . $key][0])) {
		return $custom[$prefix . $key][0];
	}
	return '';
}

// examples
$custom = get_post_custom($post->ID);
template_get_custom_field($custom, 'name'); // looks for 'custom_name'
template_get_custom_field($custom, 'thumbnail_id', ''); // looks for 'thumbnail_id'