diff --git a/optuna_dashboard/_app.py b/optuna_dashboard/_app.py
index 12571829..b7702c35 100644
--- a/optuna_dashboard/_app.py
+++ b/optuna_dashboard/_app.py
@@ -377,7 +377,7 @@ def run_server(
             DeprecationWarning,
         )
         artifact_store = ArtifactBackendToStore(artifact_backend)
-    if not is_artifact_store(artifact_store):
+    if artifact_store is not None and not is_artifact_store(artifact_store):
         artifact_store = ArtifactBackendToStore(artifact_store)
 
     app = create_app(get_storage(storage), artifact_store=artifact_store)
@@ -401,7 +401,7 @@ def wsgi(
             DeprecationWarning,
         )
         artifact_store = ArtifactBackendToStore(artifact_backend)
-    if not is_artifact_store(artifact_store):
+    if artifact_store is not None and not is_artifact_store(artifact_store):
         artifact_store = ArtifactBackendToStore(artifact_store)
 
     return create_app(get_storage(storage), artifact_store=artifact_store)
diff --git a/optuna_dashboard/artifact/_backend.py b/optuna_dashboard/artifact/_backend.py
index d90773d9..71ea38c7 100644
--- a/optuna_dashboard/artifact/_backend.py
+++ b/optuna_dashboard/artifact/_backend.py
@@ -20,6 +20,7 @@ from .._bottle_util import json_api_view
 from .._bottle_util import parse_data_uri
 from .._storage import get_trial
 
+
 if TYPE_CHECKING:
     from typing import Any
     from typing import Optional
@@ -136,12 +137,13 @@ def upload_artifact(
     mimetype: Optional[str] = None,
     encoding: Optional[str] = None,
 ) -> str:
-    """[Deprecated] Upload an artifact (files), which is associated with the trial.
+    """Upload an artifact (files), which is associated with the trial.
 
-    .. note::
+    .. warning::
 
        This function is deprecated. Please use `optuna.artifacts.upload_artifact
-       <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.upload_artifact.html>`_ instead.
+       <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.
+       upload_artifact.html>`_ instead.
 
     Example:
        .. code-block:: python
@@ -160,7 +162,8 @@ def upload_artifact(
     """
     warnings.warn(
         "This function is deprecated. Please use optuna.artifacts.upload_artifact() instead.\n"
-        "https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.upload_artifact.html",
+        "See https://optuna.readthedocs.io/en/latest/reference/generated/"
+        "optuna.artifacts.upload_artifact.html",
         DeprecationWarning,
     )
 
diff --git a/optuna_dashboard/artifact/boto3.py b/optuna_dashboard/artifact/boto3.py
index 31b6a1b5..2ef8766b 100644
--- a/optuna_dashboard/artifact/boto3.py
+++ b/optuna_dashboard/artifact/boto3.py
@@ -20,9 +20,11 @@ if TYPE_CHECKING:
 class Boto3Backend:
     """An artifact backend for S3.
 
-    .. note::
+    .. warning::
 
-       This class is deprecated. Please use `optuna.artifacts.Boto3ArtifactStore <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.Boto3ArtifactStore.html>`_ instead.",
+       This class is deprecated. Please use `optuna.artifacts.Boto3ArtifactStore
+       <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.
+       Boto3ArtifactStore.html>`_ instead.",
 
     Example:
        .. code-block:: python
@@ -51,7 +53,8 @@ class Boto3Backend:
         self._avoid_buf_copy = avoid_buf_copy
         warnings.warn(
             "Boto3Backend is deprecated. Please use optuna.artifacts.Boto3ArtifactStore instead.\n"
-            "https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.Boto3ArtifactStore.html",
+            "See https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts."
+            "Boto3ArtifactStore.html",
             DeprecationWarning,
         )
 
diff --git a/optuna_dashboard/artifact/file_system.py b/optuna_dashboard/artifact/file_system.py
index 58c795e8..bf449cc6 100644
--- a/optuna_dashboard/artifact/file_system.py
+++ b/optuna_dashboard/artifact/file_system.py
@@ -18,7 +18,8 @@ class FileSystemBackend:
     .. note::
 
        This class is deprecated. Please use `optuna.artifacts.FileSystemArtifactStore
-       <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.FileSystemArtifactStore.html>`_ instead.",
+       <https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.
+       FileSystemArtifactStore.html>`_ instead.",
 
     Example:
        .. code-block:: python
@@ -39,8 +40,9 @@ class FileSystemBackend:
     def __init__(self, base_path: str) -> None:
         self._base_path = base_path
         warnings.warn(
-            "FileSystemBackend is deprecated. Please use optuna.artifacts.FileSystemArtifactStore instead.\n"
-            "https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts.FileSystemArtifactStore.html",
+            "FileSystemBackend is deprecated. Please use FileSystemArtifactStore instead.\n"
+            "See https://optuna.readthedocs.io/en/latest/reference/generated/optuna.artifacts."
+            "FileSystemArtifactStore.html",
             DeprecationWarning,
         )
 
diff --git a/optuna_dashboard/artifact/protocol.py b/optuna_dashboard/artifact/protocol.py
index b85fc82f..3f9ffdf2 100644
--- a/optuna_dashboard/artifact/protocol.py
+++ b/optuna_dashboard/artifact/protocol.py
@@ -57,17 +57,3 @@ class ArtifactBackend(Protocol):
             artifact_id: The identifier of the artifact to remove.
         """
         ...
-
-
-class ArtifactStoreWrapper:
-    def __init__(self, artifact_backend: ArtifactBackend) -> None:
-        self._backend = artifact_backend
-
-    def open_reader(self, artifact_id: str) -> BinaryIO:
-        return self._backend.open(artifact_id)
-
-    def write(self, artifact_id: str, content_body: BinaryIO) -> None:
-        self._backend.write(artifact_id, content_body)
-
-    def remove(self, artifact_id: str) -> None:
-        self._backend.remove(artifact_id)