diff --git a/lnbits/helpers.py b/lnbits/helpers.py
index d611fb90..9eefe365 100644
--- a/lnbits/helpers.py
+++ b/lnbits/helpers.py
@@ -89,13 +89,12 @@ def url_for(endpoint: str, external: Optional[bool] = False, **params: Any) -> s
     return url
 
 
-def template_renderer(additional_folders: List = []) -> Jinja2Templates:
+def template_renderer(additional_folders: List = None) -> Jinja2Templates:
 
-    t = Jinja2Templates(
-        loader=jinja2.FileSystemLoader(
-            ["lnbits/templates", "lnbits/core/templates", *additional_folders]
-        )
-    )
+    folders = ["lnbits/templates", "lnbits/core/templates"]
+    if additional_folders:
+        folders.extend(additional_folders)
+    t = Jinja2Templates(loader=jinja2.FileSystemLoader(folders))
 
     if settings.lnbits_ad_space_enabled:
         t.env.globals["AD_SPACE"] = settings.lnbits_ad_space.split(",")
diff --git a/tools/conv.py b/tools/conv.py
index f01295fc..f589eed4 100644
--- a/tools/conv.py
+++ b/tools/conv.py
@@ -101,7 +101,7 @@ def insert_to_pg(query, data):
     connection.close()
 
 
-def migrate_core(file: str, exclude_tables: List[str] = []):
+def migrate_core(file: str, exclude_tables: List[str] = None):
     print(f"Migrating core: {file}")
     migrate_db(file, "public", exclude_tables)
     print("✅ Migrated core")
@@ -115,7 +115,7 @@ def migrate_ext(file: str):
     print(f"✅ Migrated ext: {schema}")
 
 
-def migrate_db(file: str, schema: str, exclude_tables: List[str] = []):
+def migrate_db(file: str, schema: str, exclude_tables: List[str] = None):
     # first we check if this file exists:
     assert os.path.isfile(file), f"{file} does not exist!"
 
@@ -133,7 +133,7 @@ def migrate_db(file: str, schema: str, exclude_tables: List[str] = []):
         # hard coded skip for dbversions (already produced during startup)
         if tableName == "dbversions":
             continue
-        if tableName in exclude_tables:
+        if exclude_tables and tableName in exclude_tables:
             continue
 
         columns = sq.execute(f"PRAGMA table_info({tableName})").fetchall()