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patch_history/RETRIEX_VOCABULARY_HOTFIX_README.md

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+# RetrieX Vocabulary Hotfix
+
+This patch fixes a runtime error introduced by the vocabulary centralization patch.
+
+## Fixed error
+
+`array_key_exists(): Argument #2 ($array) must be of type array, App\Config\DomainVocabularyConfig given`
+
+## Root cause
+
+`NdjsonHybridRetrieverConfig::raw()` still checked `$this->vocabulary` as if it were an array. After the vocabulary refactor, `$this->vocabulary` is a `DomainVocabularyConfig` object. Effective vocabulary fallback is already resolved before `raw()` is called, so this second `array_key_exists()` check was invalid and unnecessary.
+
+## Changed file
+
+- `src/Config/NdjsonHybridRetrieverConfig.php`
+
+## After applying
+
+Clear Symfony cache before testing.