Fix lint errors

optuna_dashboard/_app.py

@@ -10,9 +10,6 @@
 import os
 import re
 import typing
-from typing import Any
-from typing import Optional
-from typing import Union
 import warnings
 
 from bottle import Bottle
@@ -58,6 +55,11 @@
 
 
 if typing.TYPE_CHECKING:
+    from typing import Any
+    from typing import Literal
+    from typing import Optional
+    from typing import Union
+
     from _typeshed.wsgi import WSGIApplication
     from optuna.artifacts._protocol import ArtifactStore
     from optuna_dashboard.artifact.protocol import ArtifactBackend
@@ -558,14 +560,17 @@ def favicon() -> BottleViewReturn:
 
     @app.get("/static/<filename:path>")
     def send_static(filename: str) -> BottleViewReturn:
-        mimetype: bool | str = True
+        mimetype: str | Literal[True] = True
         headers: dict[str, str] | None = None
         if not debug and "gzip" in request.headers["Accept-Encoding"]:
             gz_filename = filename.strip("/\\") + ".gz"
             if cached_path_exists(os.path.join(STATIC_DIR, gz_filename)):
                 filename = gz_filename
                 headers = {"Content-Encoding": "gzip"}
-            mimetype, _ = mimetypes.guess_type(filename)
+
+            mimetype_, _ = mimetypes.guess_type(filename)
+            if mimetype_ is not None:
+                mimetype = mimetype_
         return static_file(filename, root=STATIC_DIR, mimetype=mimetype, headers=headers)
 
     register_rdb_migration_route(app, storage)

python_tests/wsgi_client.py

@@ -11,6 +11,7 @@
 
 if typing.TYPE_CHECKING:
     from sys import _OptExcInfo
+
     from _typeshed.wsgi import WSGIEnvironment
 
 
@@ -65,7 +66,9 @@ def send_request(
     status: str = ""
     response_headers: list[tuple[str, str]] = []
 
-    def start_response(status_: str, headers_: list[tuple[str, str]], exc_info: _OptExcInfo | None = None) -> None:
+    def start_response(
+        status_: str, headers_: list[tuple[str, str]], exc_info: _OptExcInfo | None = None
+    ) -> None:
         nonlocal status, response_headers
         status = status_
         response_headers = headers_