diff --git a/examples/simple/simple_ext1/application.py b/examples/simple/simple_ext1/application.py
index d420279a3c..b28d8f8781 100644
--- a/examples/simple/simple_ext1/application.py
+++ b/examples/simple/simple_ext1/application.py
@@ -31,10 +31,10 @@ class SimpleApp1(ExtensionAppJinjaMixin, ExtensionApp):
     load_other_extensions = True
 
     # Local path to static files directory.
-    static_paths = [DEFAULT_STATIC_FILES_PATH]
+    static_paths = [DEFAULT_STATIC_FILES_PATH]  # type:ignore[assignment]
 
     # Local path to templates directory.
-    template_paths = [DEFAULT_TEMPLATE_FILES_PATH]
+    template_paths = [DEFAULT_TEMPLATE_FILES_PATH]  # type:ignore[assignment]
 
     configA = Unicode("", config=True, help="Config A example.")  # noqa
 
diff --git a/examples/simple/simple_ext2/application.py b/examples/simple/simple_ext2/application.py
index b4fbbadb97..6f8498407d 100644
--- a/examples/simple/simple_ext2/application.py
+++ b/examples/simple/simple_ext2/application.py
@@ -24,10 +24,10 @@ class SimpleApp2(ExtensionAppJinjaMixin, ExtensionApp):
     load_other_extensions = True
 
     # Local path to static files directory.
-    static_paths = [DEFAULT_STATIC_FILES_PATH]
+    static_paths = [DEFAULT_STATIC_FILES_PATH]  # type:ignore[assignment]
 
     # Local path to templates directory.
-    template_paths = [DEFAULT_TEMPLATE_FILES_PATH]
+    template_paths = [DEFAULT_TEMPLATE_FILES_PATH]  # type:ignore[assignment]
 
     configD = Unicode("", config=True, help="Config D example.")  # noqa
 
diff --git a/jupyter_server/auth/identity.py b/jupyter_server/auth/identity.py
index 42c4ce839a..72f4b469e0 100644
--- a/jupyter_server/auth/identity.py
+++ b/jupyter_server/auth/identity.py
@@ -702,22 +702,24 @@ def auth_enabled(self):
 
     def get_user(self, handler: JupyterHandler) -> User | None:
         """Get the user."""
-        user = self.login_handler_class.get_user(handler)
+        user = self.login_handler_class.get_user(handler)  # type:ignore[attr-defined]
         if user is None:
             return None
         return _backward_compat_user(user)
 
     @property
     def login_available(self):
-        return self.login_handler_class.get_login_available(self.settings)
+        return self.login_handler_class.get_login_available(  # type:ignore[attr-defined]
+            self.settings
+        )
 
     def should_check_origin(self, handler: JupyterHandler) -> bool:
         """Whether we should check origin."""
-        return self.login_handler_class.should_check_origin(handler)
+        return self.login_handler_class.should_check_origin(handler)  # type:ignore[attr-defined]
 
     def is_token_authenticated(self, handler: JupyterHandler) -> bool:
         """Whether we are token authenticated."""
-        return self.login_handler_class.is_token_authenticated(handler)
+        return self.login_handler_class.is_token_authenticated(handler)  # type:ignore[attr-defined]
 
     def validate_security(
         self,
@@ -732,4 +734,6 @@ def validate_security(
             self.log.critical(_i18n("Hint: run the following command to set a password"))
             self.log.critical(_i18n("\t$ python -m jupyter_server.auth password"))
             sys.exit(1)
-        return self.login_handler_class.validate_security(app, ssl_options)
+        return self.login_handler_class.validate_security(  # type:ignore[attr-defined]
+            app, ssl_options
+        )
diff --git a/jupyter_server/extension/manager.py b/jupyter_server/extension/manager.py
index 8b2f156d52..02aad0f262 100644
--- a/jupyter_server/extension/manager.py
+++ b/jupyter_server/extension/manager.py
@@ -351,7 +351,7 @@ def load_extension(self, name):
         """Load an extension by name."""
         extension = self.extensions.get(name)
 
-        if extension.enabled:
+        if extension and extension.enabled:
             try:
                 extension.load_all_points(self.serverapp)
             except Exception as e:
diff --git a/jupyter_server/gateway/connections.py b/jupyter_server/gateway/connections.py
index 24a3375b9a..0fe973eef6 100644
--- a/jupyter_server/gateway/connections.py
+++ b/jupyter_server/gateway/connections.py
@@ -73,7 +73,7 @@ def disconnect(self):
         if self.ws is not None:
             # Close connection
             self.ws.close()
-        elif not self.ws_future.done():
+        elif self.ws_future and not self.ws_future.done():
             # Cancel pending connection.  Since future.cancel() is a noop on tornado, we'll track cancellation locally
             self.ws_future.cancel()
             self.log.debug(f"_disconnect: future cancelled, disconnected: {self.disconnected}")
@@ -93,6 +93,8 @@ async def _read_messages(self):
                     if not self.disconnected:
                         self.log.warning(f"Lost connection to Gateway: {self.kernel_id}")
                     break
+                if isinstance(message, bytes):
+                    message = message.decode("utf8")
                 self.handle_outgoing_message(
                     message
                 )  # pass back to notebook client (see self.on_open and WebSocketChannelsHandler.open)
@@ -136,7 +138,7 @@ def handle_outgoing_message(self, incoming_msg: str, *args: Any) -> None:
 
     def handle_incoming_message(self, message: str) -> None:
         """Send message to gateway server."""
-        if self.ws is None:
+        if self.ws is None and self.ws_future is not None:
             loop = IOLoop.current()
             loop.add_future(self.ws_future, lambda future: self.handle_incoming_message(message))
         else:
diff --git a/jupyter_server/gateway/gateway_client.py b/jupyter_server/gateway/gateway_client.py
index d73c0245aa..487e318923 100644
--- a/jupyter_server/gateway/gateway_client.py
+++ b/jupyter_server/gateway/gateway_client.py
@@ -156,7 +156,7 @@ def _url_validate(self, proposal):
     @default("ws_url")
     def _ws_url_default(self):
         default_value = os.environ.get(self.ws_url_env)
-        if default_value is None and self.gateway_enabled:
+        if self.url is not None and default_value is None and self.gateway_enabled:
             default_value = self.url.lower().replace("http", "ws")
         return default_value
 
@@ -462,7 +462,7 @@ def _gateway_retry_max_default(self):
     )
     gateway_token_renewer_class_env = "JUPYTER_GATEWAY_TOKEN_RENEWER_CLASS"
     gateway_token_renewer_class = Type(
-        klass=GatewayTokenRenewerBase,
+        klass=GatewayTokenRenewerBase,  # type:ignore[type-abstract]
         config=True,
         help="""The class to use for Gateway token renewal. (JUPYTER_GATEWAY_TOKEN_RENEWER_CLASS env var)""",
     )
@@ -546,7 +546,9 @@ def __init__(self, **kwargs):
         """Initialize a gateway client."""
         super().__init__(**kwargs)
         self._connection_args = {}  # initialized on first use
-        self.gateway_token_renewer = self.gateway_token_renewer_class(parent=self, log=self.log)
+        self.gateway_token_renewer = self.gateway_token_renewer_class(
+            parent=self, log=self.log
+        )  # type:ignore[operator]
 
         # store of cookies with store time
         self._cookies: ty.Dict[str, ty.Tuple[Morsel, datetime]] = {}
@@ -570,11 +572,12 @@ def init_connection_args(self):
         # Ensure any adjustments are reflected in env.
         os.environ["KERNEL_LAUNCH_TIMEOUT"] = str(GatewayClient.KERNEL_LAUNCH_TIMEOUT)
 
-        self._connection_args["headers"] = json.loads(self.headers)
-        if self.auth_header_key not in self._connection_args["headers"]:
-            self._connection_args["headers"].update(
-                {f"{self.auth_header_key}": f"{self.auth_scheme} {self.auth_token}"}
-            )
+        if self.headers:
+            self._connection_args["headers"] = json.loads(self.headers)
+            if self.auth_header_key not in self._connection_args["headers"]:
+                self._connection_args["headers"].update(
+                    {f"{self.auth_header_key}": f"{self.auth_scheme} {self.auth_token}"}
+                )
         self._connection_args["connect_timeout"] = self.connect_timeout
         self._connection_args["request_timeout"] = self.request_timeout
         self._connection_args["validate_cert"] = self.validate_cert
@@ -598,18 +601,19 @@ def load_connection_args(self, **kwargs):
 
         # Give token renewal a shot at renewing the token
         prev_auth_token = self.auth_token
-        try:
-            self.auth_token = self.gateway_token_renewer.get_token(
-                self.auth_header_key, self.auth_scheme, self.auth_token
-            )
-        except Exception as ex:
-            self.log.error(
-                f"An exception occurred attempting to renew the "
-                f"Gateway authorization token using an instance of class "
-                f"'{self.gateway_token_renewer_class}'.  The request will "
-                f"proceed using the current token value.  Exception was: {ex}"
-            )
-            self.auth_token = prev_auth_token
+        if self.auth_token:
+            try:
+                self.auth_token = self.gateway_token_renewer.get_token(
+                    self.auth_header_key, self.auth_scheme, self.auth_token
+                )
+            except Exception as ex:
+                self.log.error(
+                    f"An exception occurred attempting to renew the "
+                    f"Gateway authorization token using an instance of class "
+                    f"'{self.gateway_token_renewer_class}'.  The request will "
+                    f"proceed using the current token value.  Exception was: {ex}"
+                )
+                self.auth_token = prev_auth_token
 
         for arg, value in self._connection_args.items():
             if arg == "headers":
diff --git a/jupyter_server/gateway/managers.py b/jupyter_server/gateway/managers.py
index 919d28d854..5a09ede926 100644
--- a/jupyter_server/gateway/managers.py
+++ b/jupyter_server/gateway/managers.py
@@ -236,6 +236,8 @@ def _replace_path_kernelspec_resources(self, kernel_specs):
         This enables clients to properly route through jupyter_server to a gateway
         for kernel resources such as logo files
         """
+        if not self.parent:
+            return {}
         kernelspecs = kernel_specs["kernelspecs"]
         for kernel_name in kernelspecs:
             resources = kernelspecs[kernel_name]["resources"]
@@ -273,6 +275,8 @@ async def get_all_specs(self):
         # If different log a warning and reset the default.  However, the
         # caller of this method will still return this server's value until
         # the next fetch of kernelspecs - at which time they'll match.
+        if not self.parent:
+            return {}
         km = self.parent.kernel_manager
         remote_default_kernel_name = fetched_kspecs.get("default")
         if remote_default_kernel_name != km.default_kernel_name:
@@ -416,7 +420,7 @@ def client(self, **kwargs):
 
         # add kwargs last, for manual overrides
         kw.update(kwargs)
-        return self.client_factory(**kw)
+        return self.client_factory(**kw)  # type:ignore[operator]
 
     async def refresh_model(self, model=None):
         """Refresh the kernel model.
diff --git a/jupyter_server/serverapp.py b/jupyter_server/serverapp.py
index f9b9917772..09c2078871 100644
--- a/jupyter_server/serverapp.py
+++ b/jupyter_server/serverapp.py
@@ -1879,21 +1879,25 @@ def init_configurables(self):
         # this determination, instantiate the GatewayClient config singleton.
         self.gateway_config = GatewayClient.instance(parent=self)
 
-        if not issubclass(self.kernel_manager_class, AsyncMappingKernelManager):
+        if not issubclass(
+            self.kernel_manager_class, AsyncMappingKernelManager  # type:ignore[arg-type]
+        ):
             warnings.warn(
                 "The synchronous MappingKernelManager class is deprecated and will not be supported in Jupyter Server 3.0",
                 DeprecationWarning,
                 stacklevel=2,
             )
 
-        if not issubclass(self.contents_manager_class, AsyncContentsManager):
+        if not issubclass(
+            self.contents_manager_class, AsyncContentsManager  # type:ignore[arg-type]
+        ):
             warnings.warn(
                 "The synchronous ContentsManager classes are deprecated and will not be supported in Jupyter Server 3.0",
                 DeprecationWarning,
                 stacklevel=2,
             )
 
-        self.kernel_spec_manager = self.kernel_spec_manager_class(
+        self.kernel_spec_manager = self.kernel_spec_manager_class(  # type:ignore[operator]
             parent=self,
         )
 
@@ -1915,21 +1919,21 @@ def init_configurables(self):
                 "because jupyter-client's version does not allow them (should be >8.3.0)."
             )
 
-        self.kernel_manager = self.kernel_manager_class(**kwargs)
-        self.contents_manager = self.contents_manager_class(
+        self.kernel_manager = self.kernel_manager_class(**kwargs)  # type:ignore[operator]
+        self.contents_manager = self.contents_manager_class(  # type:ignore[operator]
             parent=self,
             log=self.log,
         )
         # Trigger a default/validation here explicitly while we still support the
         # deprecated trait on ServerApp (FIXME remove when deprecation finalized)
         self.contents_manager.preferred_dir  # noqa
-        self.session_manager = self.session_manager_class(
+        self.session_manager = self.session_manager_class(  # type:ignore[operator]
             parent=self,
             log=self.log,
             kernel_manager=self.kernel_manager,
             contents_manager=self.contents_manager,
         )
-        self.config_manager = self.config_manager_class(
+        self.config_manager = self.config_manager_class(  # type:ignore[operator]
             parent=self,
             log=self.log,
         )
@@ -1958,7 +1962,9 @@ def init_configurables(self):
                 f"Ignoring deprecated config ServerApp.login_handler_class={self.login_handler_class}."
                 " Superseded by ServerApp.identity_provider_class={self.identity_provider_class}."
             )
-        self.identity_provider = self.identity_provider_class(**identity_provider_kwargs)
+        self.identity_provider = self.identity_provider_class(
+            **identity_provider_kwargs
+        )  # type:ignore[operator]
 
         if self.identity_provider_class is LegacyIdentityProvider:
             # legacy config stored the password in tornado_settings
@@ -1979,7 +1985,7 @@ def init_configurables(self):
                 # that means it has some config that should take higher priority than deprecated ServerApp.token
                 self.log.warning("Ignoring deprecated ServerApp.token config")
 
-        self.authorizer = self.authorizer_class(
+        self.authorizer = self.authorizer_class(  # type:ignore[operator]
             parent=self, log=self.log, identity_provider=self.identity_provider
         )
 
@@ -2100,7 +2106,7 @@ def init_webapp(self):
         if not self.ssl_options:
             # could be an empty dict or None
             # None indicates no SSL config
-            self.ssl_options = None
+            self.ssl_options = None  # type:ignore[assignment]
         else:
             # SSL may be missing, so only import it if it's to be used
             import ssl
@@ -2130,7 +2136,7 @@ def init_resources(self):
         old_soft, old_hard = resource.getrlimit(resource.RLIMIT_NOFILE)
         soft = self.min_open_files_limit
         hard = old_hard
-        if old_soft < soft:
+        if soft is not None and old_soft < soft:
             if hard < soft:
                 hard = soft
             self.log.debug(
@@ -2911,7 +2917,7 @@ async def _cleanup(self):
         await self.cleanup_extensions()
         await self.cleanup_kernels()
         try:
-            await self.kernel_websocket_connection_class.close_all()
+            await self.kernel_websocket_connection_class.close_all()  # type:ignore[attr-defined]
         except AttributeError:
             # This can happen in two different scenarios:
             #
diff --git a/jupyter_server/services/contents/filecheckpoints.py b/jupyter_server/services/contents/filecheckpoints.py
index 00f36f61be..f6d1ef44e7 100644
--- a/jupyter_server/services/contents/filecheckpoints.py
+++ b/jupyter_server/services/contents/filecheckpoints.py
@@ -43,10 +43,9 @@ class FileCheckpoints(FileManagerMixin, Checkpoints):
     root_dir = Unicode(config=True)
 
     def _root_dir_default(self):
-        try:
-            return self.parent.root_dir
-        except AttributeError:
+        if not self.parent:
             return os.getcwd()
+        return self.parent.root_dir
 
     # ContentsManager-dependent checkpoint API
     def create_checkpoint(self, contents_mgr, path):
diff --git a/jupyter_server/services/contents/filemanager.py b/jupyter_server/services/contents/filemanager.py
index 4ecfa6e00f..4ddf9cd721 100644
--- a/jupyter_server/services/contents/filemanager.py
+++ b/jupyter_server/services/contents/filemanager.py
@@ -48,10 +48,9 @@ class FileContentsManager(FileManagerMixin, ContentsManager):
 
     @default("root_dir")
     def _default_root_dir(self):
-        try:
-            return self.parent.root_dir
-        except AttributeError:
+        if not self.parent:
             return os.getcwd()
+        return self.parent.root_dir
 
     @validate("root_dir")
     def _validate_root_dir(self, proposal):
@@ -65,6 +64,8 @@ def _validate_root_dir(self, proposal):
 
     @default("preferred_dir")
     def _default_preferred_dir(self):
+        if not self.parent:
+            return ""
         try:
             value = self.parent.preferred_dir
             if value == self.parent.root_dir:
diff --git a/jupyter_server/services/contents/manager.py b/jupyter_server/services/contents/manager.py
index 9482d42884..dc9c754f84 100644
--- a/jupyter_server/services/contents/manager.py
+++ b/jupyter_server/services/contents/manager.py
@@ -100,11 +100,12 @@ def _validate_preferred_dir(self, proposal):
             raise TraitError(e.log_message) from e
         if not dir_exists:
             raise TraitError(_i18n("Preferred directory not found: %r") % value)
-        try:
-            if value != self.parent.preferred_dir:
-                self.parent.preferred_dir = os.path.join(self.root_dir, *value.split("/"))
-        except (AttributeError, TraitError):
-            pass
+        if self.parent:
+            try:
+                if value != self.parent.preferred_dir:
+                    self.parent.preferred_dir = os.path.join(self.root_dir, *value.split("/"))
+            except TraitError:
+                pass
         return value
 
     allow_hidden = Bool(False, config=True, help="Allow access to hidden files")
@@ -324,7 +325,7 @@ def run_post_save_hooks(self, model, os_path):
 
     @default("checkpoints")
     def _default_checkpoints(self):
-        return self.checkpoints_class(**self.checkpoints_kwargs)
+        return self.checkpoints_class(**self.checkpoints_kwargs)  # type:ignore[operator]
 
     @default("checkpoints_kwargs")
     def _default_checkpoints_kwargs(self):
@@ -760,7 +761,7 @@ class AsyncContentsManager(ContentsManager):
 
     @default("checkpoints")
     def _default_checkpoints(self):
-        return self.checkpoints_class(**self.checkpoints_kwargs)
+        return self.checkpoints_class(**self.checkpoints_kwargs)  # type:ignore[operator]
 
     @default("checkpoints_kwargs")
     def _default_checkpoints_kwargs(self):
diff --git a/jupyter_server/services/events/handlers.py b/jupyter_server/services/events/handlers.py
index 3f3a5c64c2..9f58692ea3 100644
--- a/jupyter_server/services/events/handlers.py
+++ b/jupyter_server/services/events/handlers.py
@@ -44,7 +44,8 @@ async def get(self, *args, **kwargs):
         """Get an event socket."""
         self.pre_get()
         res = super().get(*args, **kwargs)
-        await res
+        if res is not None:
+            await res
 
     async def event_listener(self, logger: EventLogger, schema_id: str, data: dict) -> None:
         """Write an event message."""
diff --git a/jupyter_server/services/kernels/connection/channels.py b/jupyter_server/services/kernels/connection/channels.py
index c90964ed82..fca4bbd31c 100644
--- a/jupyter_server/services/kernels/connection/channels.py
+++ b/jupyter_server/services/kernels/connection/channels.py
@@ -6,7 +6,7 @@
 from concurrent.futures import Future
 from textwrap import dedent
 from typing import Dict as Dict_t
-from typing import MutableSet
+from typing import MutableSet, cast
 
 from jupyter_client import protocol_version as client_protocol_version
 from tornado import gen, web
@@ -85,6 +85,8 @@ class ZMQChannelsWebsocketConnection(BaseKernelWebsocketConnection):
         ),
     )
 
+    websocket_handler = Instance(KernelWebsocketHandler)
+
     @property
     def write_message(self):
         """Alias to the websocket handler's write_message method."""
@@ -283,7 +285,9 @@ async def _register_session(self):
         if (
             self.kernel_id in self.multi_kernel_manager
         ):  # only update open sessions if kernel is actively managed
-            self._open_sessions[self.session_key] = self.websocket_handler
+            self._open_sessions[self.session_key] = cast(
+                KernelWebsocketHandler, self.websocket_handler
+            )
 
     async def prepare(self):
         """Prepare a kernel connection."""
diff --git a/jupyter_server/services/kernels/kernelmanager.py b/jupyter_server/services/kernels/kernelmanager.py
index ca57228753..312abeb73a 100644
--- a/jupyter_server/services/kernels/kernelmanager.py
+++ b/jupyter_server/services/kernels/kernelmanager.py
@@ -72,10 +72,9 @@ def _default_kernel_manager_class(self):
 
     @default("root_dir")
     def _default_root_dir(self):
-        try:
-            return self.parent.root_dir
-        except AttributeError:
+        if not self.parent:
             return os.getcwd()
+        return self.parent.root_dir
 
     @validate("root_dir")
     def _update_root_dir(self, proposal):
diff --git a/jupyter_server/traittypes.py b/jupyter_server/traittypes.py
index 536f2b24ab..bd6f28a36b 100644
--- a/jupyter_server/traittypes.py
+++ b/jupyter_server/traittypes.py
@@ -114,7 +114,7 @@ def _resolve_classes(self):
                 self.importable_klasses.append(klass)
 
         if isinstance(self.default_value, str):
-            self.default_value = self._resolve_string(self.default_value)
+            self.default_value = self._resolve_string(self.default_value)  # type:ignore[arg-type]
 
     def default_value_repr(self):
         """The default value repr."""
diff --git a/pyproject.toml b/pyproject.toml
index 5ba07d5fb4..47695dc9b5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -104,7 +104,7 @@ nowarn = "test -W default {args}"
 
 [tool.hatch.envs.typing]
 features = ["test"]
-dependencies = [ "mypy>=1.5.1" ]
+dependencies = [ "mypy>=1.5.1", "traitlets>=5.10.1" ]
 [tool.hatch.envs.typing.scripts]
 test = "mypy --install-types --non-interactive {args:.}"
 
diff --git a/tests/extension/mockextensions/app.py b/tests/extension/mockextensions/app.py
index 77010c1a56..51757ae9f2 100644
--- a/tests/extension/mockextensions/app.py
+++ b/tests/extension/mockextensions/app.py
@@ -45,7 +45,7 @@ def get(self):
 class MockExtensionApp(ExtensionAppJinjaMixin, ExtensionApp):
     name = "mockextension"
     template_paths = List().tag(config=True)
-    static_paths = [STATIC_PATH]
+    static_paths = [STATIC_PATH]  # type:ignore[assignment]
     mock_trait = Unicode("mock trait", config=True)
     loaded = False