template: type BaseLoader autoescape kwarg as optional

diff --git a/tornado/template.py b/tornado/template.py
index d53e977c5e48d8e212a076b034abefd958a2548b..2340cdbefd5e1621b38ecbbfc14c016480d4064f 100644 (file)
--- a/tornado/template.py
+++ b/tornado/template.py
@@ -399,7 +399,7 @@ class BaseLoader(object):
 
     def __init__(
         self,
-        autoescape: str = _DEFAULT_AUTOESCAPE,
+        autoescape: Optional[str] = _DEFAULT_AUTOESCAPE,
         namespace: Optional[Dict[str, Any]] = None,
         whitespace: Optional[str] = None,
     ) -> None: