DDST-416: Add fall-back logic for default image

src/Plugin/search_api/processor/DgiImageDiscovery.php

@@ -131,8 +131,51 @@ public function addFieldValues(ItemInterface $item) {
         if ($generated_url) {
           $field->addValue($generated_url->getGeneratedUrl());
         }
+        else {
+          // Fallback to default image if URL generation fails.
+          $default_image_url = $this->getDefaultImageFromTaxonomy($entity, $image_style_name);
+          if ($default_image_url) {
+            $field->addValue($default_image_url);
+          }
+        }
       }
     }
   }
 
+  /**
+   * Gets the default image URL from the taxonomy term.
+   *
+   * @param \Drupal\node\NodeInterface $node
+   *   The node to get the default image from.
+   * @param string $image_style_name
+   *   The image style to use.
+   *
+   * @return string|null
+   *   The default image URL or null if not found.
+   */
+  protected function getDefaultImageFromTaxonomy(NodeInterface $node, string $image_style_name) {
+    $default_image_url = NULL;
+    $model_terms = $node->get('field_model')->referencedEntities();
+
+    foreach ($model_terms as $term) {
+      if ($term instanceof \Drupal\taxonomy\Entity\Term) {
+        // Load the media entity referenced by the field_defaultimage.
+        $media = $term->get('field_defaultimage')->entity;
+        if ($media instanceof \Drupal\media\Entity\Media) {
+          // Load the file entity from the media entity.
+          $file = $media->get('field_media_image')->entity;
+          if ($file instanceof \Drupal\file\Entity\File) {
+            // Use the provided image style.
+            $default_image_url = $this->entityTypeManager->getStorage('image_style')->load($image_style_name)
+              ->buildUrl($file->getFileUri());
+            // Return the first default image found, if applicable.
+            break;
+          }
+        }
+      }
+    }
+
+    return $default_image_url;
+  }
+
 }