Real JSON null for empty product feature; SSR warm-cache button and CLI

Ticket 0068-FE: ProductFeatureJsonRenderer returned json_encode(null), which headless passes on as the STRING null (it only decodes object/array-looking strings) and crashed the front end. It now returns an empty string and the TypoScript field sets ifEmptyReturnNull = 1, giving a real JSON null. No other renderer used the pattern. Ticket 0066-FE: SsrPurgeService::warm() posts to the node /__warm endpoint (derived from SSR_PURGE_ENDPOINT, same secret), exposed as a Warm cache button with confirmation in the VITEC SSR module, a Cache warming progress row fed by /__health, and the CLI vitec:ssr-warm [paths]. Warm runs are deliberately not written to the purge log. Verified: two-path run 2/2 done, affected page delivers productfeature null.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

packages/vitec/Classes/UserFunc/ProductFeatureJsonRenderer.php

@@ -21,6 +21,12 @@ use TYPO3\CMS\Core\Utility\GeneralUtility;
  *
  * Extends ProductListJsonRenderer purely to reuse its serializeProduct()
  * and image handling - same filters, same shape, one source of truth.
+ *
+ * "No product" returns an EMPTY STRING, never json_encode(null): headless
+ * only decodes strings that look like objects/arrays, so the text "null"
+ * went out as the string "null" and crashed the front end (ticket
+ * 0068-FE). The TypoScript sets ifEmptyReturnNull = 1 on this field,
+ * which turns the empty string into a real JSON null.
  */
 final class ProductFeatureJsonRenderer extends ProductListJsonRenderer
 {
@@ -33,7 +39,7 @@ final class ProductFeatureJsonRenderer extends ProductListJsonRenderer
                 ->convertFlexFormContentToArray((string)($row['pi_flexform'] ?? ''));
             $productUid = (int)($flexFormData['settings']['product'] ?? 0);
             if ($productUid <= 0) {
-                return (string)json_encode(null);
+                return '';
             }
 
             $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)
@@ -47,12 +53,12 @@ final class ProductFeatureJsonRenderer extends ProductListJsonRenderer
                 )
                 ->executeQuery()->fetchAssociative();
             if (!$product) {
-                return (string)json_encode(null);
+                return '';
             }
 
             return (string)json_encode($this->serializeProduct($product), JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
         } catch (\Throwable) {
-            return (string)json_encode(null);
+            return '';
         }
     }
 }