feat: harden xml parsing to avoid uncaught errors

src/BusProNet/XmlParser/AbstractParser.php

@@ -47,4 +47,23 @@ abstract class AbstractParser
 
         return $this->stringToArray($node->text(), $separator);
     }
+
+    protected function getAttrOrNullValue(Crawler $node, string $attribute): ?string
+    {
+        if (0 === $node->count()) {
+            return null;
+        }
+
+        return $node->attr($attribute);
+    }
+
+    protected function getRequiredAttrValue(Crawler $node, string $attribute, string $context): string
+    {
+        $value = $this->getAttrOrNullValue($node, $attribute);
+        if (null === $value || '' === trim($value)) {
+            throw new \InvalidArgumentException(sprintf('Missing required attribute "%s" in %s.', $attribute, $context));
+        }
+
+        return $value;
+    }
 }