Add explicit exception handling for missing association type codes

This commit addresses PR feedback to improve error handling by throwing
an explicit exception instead of silently continuing when an association
type code cannot be retrieved.

Changes made:
- Created ProductAssociationTypeNotFoundException with descriptive message
  including the association ID for better debugging
- Updated ProductNormalizer to throw the exception instead of silently
  skipping associations with null type codes
- Added unit test to verify the exception is thrown when type code is null

This change improves debugging and makes error conditions explicit rather
than silently failing, which is better for production systems where missing
association type codes likely indicate a data integrity issue that should
be addressed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude

src/Api/Normalizer/ProductNormalizer.php

@@ -5,6 +5,7 @@
 namespace CommerceWeavers\SyliusAlsoBoughtPlugin\Api\Normalizer;
 
 use CommerceWeavers\SyliusAlsoBoughtPlugin\Doctrine\Query\GetAssociationTypeCodeByAssociationIdQueryInterface;
+use CommerceWeavers\SyliusAlsoBoughtPlugin\Exception\ProductAssociationTypeNotFoundException;
 use Sylius\Bundle\ApiBundle\Converter\IriToIdentifierConverterInterface;
 use Symfony\Component\Serializer\Normalizer\ContextAwareNormalizerInterface;
 use Symfony\Component\Serializer\Normalizer\NormalizerAwareInterface;
@@ -39,7 +40,7 @@ public function normalize($object, string $format = null, array $context = []):
             $associationTypeCode = $this->getAssociationTypeCodeByAssociationIdQuery->get((int) $id);
 
             if (null === $associationTypeCode) {
-                continue;
+                throw new ProductAssociationTypeNotFoundException((int) $id);
             }
 
             $object['associations'][$associationTypeCode] = $association;

src/Exception/ProductAssociationTypeNotFoundException.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CommerceWeavers\SyliusAlsoBoughtPlugin\Exception;
+
+final class ProductAssociationTypeNotFoundException extends \RuntimeException
+{
+    public function __construct(int $associationId)
+    {
+        parent::__construct(sprintf('Product association type not found for association with id "%d".', $associationId));
+    }
+}

tests/Unit/Api/Normalizer/ProductNormalizerTest.php

@@ -6,6 +6,7 @@
 
 use CommerceWeavers\SyliusAlsoBoughtPlugin\Api\Normalizer\ProductNormalizer;
 use CommerceWeavers\SyliusAlsoBoughtPlugin\Doctrine\Query\GetAssociationTypeCodeByAssociationIdQueryInterface;
+use CommerceWeavers\SyliusAlsoBoughtPlugin\Exception\ProductAssociationTypeNotFoundException;
 use PHPUnit\Framework\TestCase;
 use Prophecy\PhpUnit\ProphecyTrait;
 use Sylius\Bundle\ApiBundle\Converter\IriToIdentifierConverterInterface;
@@ -54,6 +55,35 @@ public function testItAddsAssociationsTypesToProductResponse(): void
             $normalizer->normalize($product->reveal())
         );
     }
+
+    public function testItThrowsExceptionWhenAssociationTypeCodeIsNull(): void
+    {
+        $baseNormalizer = $this->prophesize(ProductNormalizerInterface::class);
+        $query = $this->prophesize(GetAssociationTypeCodeByAssociationIdQueryInterface::class);
+        $iriToIdentifierConverter = $this->prophesize(IriToIdentifierConverterInterface::class);
+
+        $normalizer = new ProductNormalizer(
+            $baseNormalizer->reveal(),
+            $query->reveal(),
+            $iriToIdentifierConverter->reveal(),
+        );
+
+        $product = $this->prophesize(Product::class);
+        $baseNormalizer->normalize($product->reveal(), null, [])->willReturn([
+            'code' => 'product_code',
+            'associations' => [
+                '/api/v2/product-associations/1',
+            ],
+        ]);
+
+        $iriToIdentifierConverter->getIdentifier('/api/v2/product-associations/1')->willReturn('1');
+        $query->get(1)->willReturn(null);
+
+        $this->expectException(ProductAssociationTypeNotFoundException::class);
+        $this->expectExceptionMessage('Product association type not found for association with id "1".');
+
+        $normalizer->normalize($product->reveal());
+    }
 }
 
 interface ProductNormalizerInterface extends ContextAwareNormalizerInterface, NormalizerAwareInterface