EDD Required Address Fields But Not on Free Downloads

gistfile1.php

<?php
/**
 * Mark address field required except for free downloads
 */
function pw_edd_purchase_form_required_fields( $required_fields ) {
	$cart_total = edd_get_cart_total();
	$required_fields['card_address'] = array(
		'error_id' => 'invalid_adress',
		'error_message' => __( 'Please enter your address.', 'edd' )
	);
	return 0 != $cart_total ? $required_fields : array();
}
add_filter( 'edd_purchase_form_required_fields', 'pw_edd_purchase_form_required_fields' );