Woocommerce: non numeric value encountered in .. class-wc-shipping-flat-rate-boxes.php

After PHP 7 upgrade

Warning: A non-numeric value encountered in /home/mecha4ma/public_html/wp-content/plugins/woocommerce-shipping-flat-rate-boxes/includes/class-wc-shipping-flat-rate-boxes.php on line 344

Line 344:

// add fee
$cost += $this->get_fee( $this->fee, $package->value );

Change to:

        // add fee
$cost += (float)$this->get_fee( $this->fee, $package->value );