fix：修复知识库查询为空时，NPE错误

src/main/java/cn/com/poc/thirdparty/resource/demand/ai/aggregate/impl/DemandKnowledgeServiceImpl.java

@@ -93,6 +93,9 @@ public class DemandKnowledgeServiceImpl implements DemandKnowledgeService {
         if (null == searchKnowledgeResult) {
             throw new I18nMessageException("exception/query.knowledge.base.exception");
         }
+        if (CollectionUtils.isEmpty(searchKnowledgeResult.getDocuments())) {
+            return new ArrayList<String>();
+        }
         return searchKnowledgeResult.getDocuments();
     }