chore: major code cleanup and type safety using phpstan

src/BusProNet/XmlParser/ProductsParser.php

@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 
 namespace App\BusProNet\XmlParser;
 
@@ -15,10 +16,11 @@ class ProductsParser extends AbstractParser
         $result
             ->filterXPath('//produkte/produkt')
             ->each(function (Crawler $node) use (&$products) {
-                if (false === empty($node->attr('code'))) {
+                $code = $node->attr('code');
+                if (null !== $code && '' !== $code) {
                     $product = new Product();
                     $product->id = (int) $node->attr('id');
-                    $product->code = (string) $node->attr('code');
+                    $product->code = $code;
                     $product->name = (string) $node->attr('bezeichnung');
 
                     $products[$product->id] = $product;