diff --git a/optuna_dashboard/_app.py b/optuna_dashboard/_app.py
index 60eccd8d..f582d5e5 100644
--- a/optuna_dashboard/_app.py
+++ b/optuna_dashboard/_app.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-from datetime import datetime
 import functools
 import logging
 import os
@@ -263,7 +262,7 @@ def create_app(
             }
 
         note.save_note_with_version(storage, study_id, None, req_note_ver, req_note_body)
-        response.status = 204  # No contenthttps://github.com/microsoft/pyright/blob/main/docs/configuration.md#reportUndefinedVariable
+        response.status = 204  # No content
         return {}
 
     @app.post("/api/studies/<study_id:int>/preference")
diff --git a/optuna_dashboard/_serializer.py b/optuna_dashboard/_serializer.py
index 52ca620c..19ceb19b 100644
--- a/optuna_dashboard/_serializer.py
+++ b/optuna_dashboard/_serializer.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-from datetime import datetime
 import json
 from typing import Any
 from typing import TYPE_CHECKING
diff --git a/optuna_dashboard/ts/components/App.tsx b/optuna_dashboard/ts/components/App.tsx
index e904ae30..8adf8895 100644
--- a/optuna_dashboard/ts/components/App.tsx
+++ b/optuna_dashboard/ts/components/App.tsx
@@ -97,7 +97,7 @@ export const App: FC = () => {
                   }
                 />
                 <Route
-                  path={URL_PREFIX + "/studies/:studyId/preferenceHistory"}
+                  path={URL_PREFIX + "/studies/:studyId/preference-history"}
                   element={
                     <StudyDetail
                       toggleColorMode={toggleColorMode}
diff --git a/optuna_dashboard/ts/components/AppDrawer.tsx b/optuna_dashboard/ts/components/AppDrawer.tsx
index 9dd4bd36..cdf331bc 100644
--- a/optuna_dashboard/ts/components/AppDrawer.tsx
+++ b/optuna_dashboard/ts/components/AppDrawer.tsx
@@ -219,7 +219,7 @@ export const AppDrawer: FC<{
               >
                 <ListItemButton
                   component={Link}
-                  to={`${URL_PREFIX}/studies/${studyId}/preferenceHistory`}
+                  to={`${URL_PREFIX}/studies/${studyId}/preference-history`}
                   sx={styleListItemButton}
                   selected={page === "analytics"}
                 >
diff --git a/python_tests/test_preferential_history.py b/python_tests/test_preferential_history.py
index 3448abc3..64591783 100644
--- a/python_tests/test_preferential_history.py
+++ b/python_tests/test_preferential_history.py
@@ -1,12 +1,11 @@
 from __future__ import annotations
 
-from datetime import datetime
 from typing import Callable
 
 from optuna_dashboard._preferential_history import report_history
-from optuna_dashboard.preferential._system_attrs import _SYSTEM_ATTR_PREFIX_PREFERENCE
 from optuna_dashboard._serializer import serialize_preference_history
 from optuna_dashboard.preferential import create_study
+from optuna_dashboard.preferential._system_attrs import _SYSTEM_ATTR_PREFIX_PREFERENCE
 
 from .storage_supplier import parametrize_storages
 from .storage_supplier import StorageSupplier