Custom field – setting a default value

I have some php that I run in a php sidebar widget. It’s getting along well with the custom field feature

I have this in my functions.php file

function get_custom_field_value($szKey, $bPrint = false) {
	global $post;
	$szValue = get_post_meta($post->ID, $szKey, true);
	if ( $bPrint == false ) return $szValue; else echo $szValue;
}

Then use this to get the key value

$_REQUEST['my_search'] = get_custom_field_value('my-key', false);

But now I would like to have some default value set if there is not a value for the key on a given page.