agent template upgrade (#3060)

### What problem does this PR solve?
#3056

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

agent/component/retrieval.py

         self.check_decimal_float(self.similarity_threshold, "[Retrieval] Similarity threshold")
         self.check_decimal_float(self.keywords_similarity_weight, "[Retrieval] Keywords similarity weight")
         self.check_positive_number(self.top_n, "[Retrieval] Top N")
-        self.check_empty(self.kb_ids, "[Retrieval] Knowledge bases")
 
 
 class Retrieval(ComponentBase, ABC):
     component_name = "Retrieval"
 
     def _run(self, history, **kwargs):
-        # query = []
-        # for role, cnt in history[::-1][:self._param.message_history_window_size]:
-        #     if role != "user":continue
-        #     query.append(cnt)
-        # # query = "\n".join(query)
-        # query = query[0]
         query = self.get_input()
         query = str(query["content"][0]) if "content" in query else ""
 
         kbs = KnowledgebaseService.get_by_ids(self._param.kb_ids)
         if not kbs:
-            raise ValueError("Can't find knowledgebases by {}".format(self._param.kb_ids))
+            return Retrieval.be_output("")
+
         embd_nms = list(set([kb.embd_id for kb in kbs]))
         assert len(embd_nms) == 1, "Knowledge bases use different embedding models."