diff --git a/server/knowledge_base/kb_service/base.py b/server/knowledge_base/kb_service/base.py
index a81474f..d823740 100644
--- a/server/knowledge_base/kb_service/base.py
+++ b/server/knowledge_base/kb_service/base.py
@@ -278,15 +278,10 @@ class KBServiceFactory:
             return DefaultKBService(kb_name)
 
     @staticmethod
-    def get_service_by_name(kb_name: str,
-                            default_vs_type: SupportedVSType = SupportedVSType.FAISS,
-                            default_embed_model: str = EMBEDDING_MODEL,
-                            ) -> KBService:
+    def get_service_by_name(kb_name: str) -> KBService:
         _, vs_type, embed_model = load_kb_from_db(kb_name)
-        if vs_type is None:  # faiss knowledge base not in db
-            vs_type = default_vs_type
-        if embed_model is None:
-            embed_model = default_embed_model
+        if _ is None:  # kb not in db, just return None
+            return None
         return KBServiceFactory.get_service(kb_name, vs_type, embed_model)
 
     @staticmethod
@@ -331,6 +326,9 @@ def get_kb_details() -> List[Dict]:
 
 def get_kb_file_details(kb_name: str) -> List[Dict]:
     kb = KBServiceFactory.get_service_by_name(kb_name)
+    if kb is None:
+        return []
+
     files_in_folder = list_files_from_folder(kb_name)
     files_in_db = kb.list_files()
     result = {}
diff --git a/server/knowledge_base/migrate.py b/server/knowledge_base/migrate.py
index 146dc77..0c21946 100644
--- a/server/knowledge_base/migrate.py
+++ b/server/knowledge_base/migrate.py
@@ -157,7 +157,7 @@ def prune_db_docs(kb_names: List[str]):
     """
     for kb_name in kb_names:
         kb = KBServiceFactory.get_service_by_name(kb_name)
-        if kb and kb.exists():
+        if kb is not None:
             files_in_db = kb.list_files()
             files_in_folder = list_files_from_folder(kb_name)
             files = list(set(files_in_db) - set(files_in_folder))
@@ -175,7 +175,7 @@ def prune_folder_files(kb_names: List[str]):
     """
     for kb_name in kb_names:
         kb = KBServiceFactory.get_service_by_name(kb_name)
-        if kb and kb.exists():
+        if kb is not None:
             files_in_db = kb.list_files()
             files_in_folder = list_files_from_folder(kb_name)
             files = list(set(files_in_folder) - set(files_in_db))
diff --git a/tests/test_migrate.py b/tests/test_migrate.py
index d694b02..7195dd3 100644
--- a/tests/test_migrate.py
+++ b/tests/test_migrate.py
@@ -33,7 +33,7 @@ def test_recreate_vs():
     folder2db([kb_name], "recreate_vs")
 
     kb = KBServiceFactory.get_service_by_name(kb_name)
-    assert kb.exists()
+    assert kb and kb.exists()
 
     files = kb.list_files()
     print(files)