diff --git a/app/tree/environment.py b/app/tree/environment.py
index b89df7b..56aa2e7 100644
--- a/app/tree/environment.py
+++ b/app/tree/environment.py
@@ -11,6 +11,7 @@ from __future__ import annotations
 
 import re
 from pathlib import Path
+from collections.abc import Iterable
 from typing import TYPE_CHECKING, Any
 
 import numpy as np
@@ -94,7 +95,7 @@ _ENTITY_FIELDS_BY_LEVEL: dict[str, tuple[str, ...]] = {
 }
 
 
-def _clean_join(values: object) -> str:
+def _clean_join(values: Iterable[object] | None) -> str:
     """过滤非空字符串、去重（保序）、分号拼接；无有效值返回空串。
 
     参数: