MAGETWO-91501: Invoice and Shipping PDF does not show Size 0 for child product

- Change check custom option value

Author: YuliyaLabudova

app/code/Magento/Sales/Model/Order/Pdf/Items/Invoice/DefaultInvoice.php

@@ -127,7 +127,7 @@ public function draw()
                     'feed' => 35,
                 ];
 
-                if ($option['value']) {
+                if ($option['value'] !== null) {
                     if (isset($option['print_value'])) {
                         $printValue = $option['print_value'];
                     } else {