diff --git a/oslo_middleware/base.py b/oslo_middleware/base.py
index b1a2883..dab966e 100644
--- a/oslo_middleware/base.py
+++ b/oslo_middleware/base.py
@@ -73,7 +73,7 @@ class ConfigurableMiddleware:
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         """Base middleware constructor
diff --git a/oslo_middleware/basic_auth.py b/oslo_middleware/basic_auth.py
index 6b7fd3b..9114c28 100644
--- a/oslo_middleware/basic_auth.py
+++ b/oslo_middleware/basic_auth.py
@@ -55,7 +55,7 @@ class BasicAuthMiddleware(base.ConfigurableMiddleware):
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)
diff --git a/oslo_middleware/cors.py b/oslo_middleware/cors.py
index 521e8bc..7926bff 100644
--- a/oslo_middleware/cors.py
+++ b/oslo_middleware/cors.py
@@ -155,7 +155,7 @@ class CORS(base.ConfigurableMiddleware):
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)
diff --git a/oslo_middleware/healthcheck/__init__.py b/oslo_middleware/healthcheck/__init__.py
index 770e040..5e95d11 100644
--- a/oslo_middleware/healthcheck/__init__.py
+++ b/oslo_middleware/healthcheck/__init__.py
@@ -399,7 +399,7 @@ Reason
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)
@@ -485,7 +485,7 @@ Reason
         """
         conf = global_conf.copy() if global_conf else {}
         conf.update(local_conf)
-        middleware = cls(None, conf)  # type: ignore
+        middleware = cls(None, conf)
         middleware._ignore_path = True
         return middleware
 
diff --git a/oslo_middleware/http_proxy_to_wsgi.py b/oslo_middleware/http_proxy_to_wsgi.py
index 11435d3..a72479a 100644
--- a/oslo_middleware/http_proxy_to_wsgi.py
+++ b/oslo_middleware/http_proxy_to_wsgi.py
@@ -43,7 +43,7 @@ class HTTPProxyToWSGI(base.ConfigurableMiddleware):
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)
diff --git a/oslo_middleware/sizelimit.py b/oslo_middleware/sizelimit.py
index 87cbda3..a322ed0 100644
--- a/oslo_middleware/sizelimit.py
+++ b/oslo_middleware/sizelimit.py
@@ -84,7 +84,7 @@ class RequestBodySizeLimiter(base.ConfigurableMiddleware):
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)
diff --git a/oslo_middleware/stats.py b/oslo_middleware/stats.py
index 1fb8921..9f94da3 100644
--- a/oslo_middleware/stats.py
+++ b/oslo_middleware/stats.py
@@ -73,7 +73,7 @@ class StatsMiddleware(base.ConfigurableMiddleware):
 
     def __init__(
         self,
-        application: WSGIApplication,
+        application: WSGIApplication | None,
         conf: dict[str, ty.Any] | cfg.ConfigOpts | None = None,
     ) -> None:
         super().__init__(application, conf)