Ignore exception of empty index. (#5030)

### What problem does this PR solve?

### Type of change


- [x] Refactoring

api/apps/kb_app.py

@@ -14,7 +14,6 @@
 #  limitations under the License.
 #
 import json
-import logging
 import os
 
 from flask import request
@@ -300,11 +299,12 @@ def knowledge_graph(kb_id):
         "kb_id": [kb_id],
         "knowledge_graph_kwd": ["graph"]
     }
+
     obj = {"graph": {}, "mind_map": {}}
-    try:
-        sres = settings.retrievaler.search(req, search.index_name(kb.tenant_id), [kb_id])
-    except Exception as e:
-        logging.exception(e)
+    if not settings.docStoreConn.indexExist(search.index_name(kb.tenant_id)):
+        return get_json_result(data=obj)
+    sres = settings.retrievaler.search(req, search.index_name(kb.tenant_id), [kb_id])
+    if not len(sres.ids):
         return get_json_result(data=obj)
 
     for id in sres.ids[:1]:

rag/utils/es_conn.py

@@ -113,7 +113,7 @@ class ESConnection(DocStoreConnection):
         except Exception:
             logger.exception("ESConnection.deleteIdx error %s" % (indexName))
 
-    def indexExist(self, indexName: str, knowledgebaseId: str) -> bool:
+    def indexExist(self, indexName: str, knowledgebaseId: str = None) -> bool:
         s = Index(indexName, self.es)
         for i in range(ATTEMPT_TIME):
             try: