diff --git a/pymodbus/client/base.py b/pymodbus/client/base.py
index 232666289..88ddc02a5 100644
--- a/pymodbus/client/base.py
+++ b/pymodbus/client/base.py
@@ -123,10 +123,10 @@ def __init__(  # pylint: disable=too-many-arguments
         self.transaction = DictTransactionManager(
             self, retries=retries, retry_on_empty=retry_on_empty, **kwargs
         )
-        self.reconnect_delay_current = self.params.reconnect_delay
+        self.reconnect_delay_current = self.params.reconnect_delay or 0
         self.use_udp = False
         self.state = ModbusTransactionState.IDLE
-        self.last_frame_end: float = 0
+        self.last_frame_end: float | None = 0
         self.silent_interval: float = 0
 
     # ----------------------------------------------------------------------- #
@@ -165,7 +165,7 @@ def idle_time(self) -> float:
             return 0
         return self.last_frame_end + self.silent_interval
 
-    def execute(self, request: ModbusRequest = None) -> ModbusResponse:
+    def execute(self, request: ModbusRequest | None = None) -> ModbusResponse:
         """Execute request and get response (call **sync/async**).
 
         :param request: The request to process
@@ -211,7 +211,7 @@ async def async_execute(self, request=None):
 
         return resp
 
-    def callback_data(self, data: bytes, addr: tuple = None) -> int:
+    def callback_data(self, data: bytes, addr: tuple | None = None) -> int:
         """Handle received data
 
         returns number of bytes consumed
diff --git a/pymodbus/client/mixin.py b/pymodbus/client/mixin.py
index ba531c6b3..84ddfa237 100644
--- a/pymodbus/client/mixin.py
+++ b/pymodbus/client/mixin.py
@@ -525,7 +525,7 @@ def read_fifo_queue(
     # code 0x2B sub 0x0D: CANopen General Reference Request and Response, NOT IMPLEMENTED
 
     def read_device_information(
-        self, read_code: int = None, object_id: int = 0x00, **kwargs: Any
+        self, read_code: int | None = None, object_id: int = 0x00, **kwargs: Any
     ) -> ModbusResponse | Awaitable[ModbusResponse]:
         """Read FIFO queue (code 0x2B sub 0x0E).
 
diff --git a/pymodbus/client/serial.py b/pymodbus/client/serial.py
index c379e31da..3191fa7c1 100644
--- a/pymodbus/client/serial.py
+++ b/pymodbus/client/serial.py
@@ -169,8 +169,7 @@ def __init__(
         """Initialize Modbus Serial Client."""
         self.transport = None
         kwargs["use_sync"] = True
-        ModbusBaseClient.__init__(
-            self,
+        super().__init__(
             framer,
             CommType=CommType.SERIAL,
             host=port,
diff --git a/pymodbus/server/async_io.py b/pymodbus/server/async_io.py
index 4eb6654ea..4b17426ec 100644
--- a/pymodbus/server/async_io.py
+++ b/pymodbus/server/async_io.py
@@ -230,7 +230,7 @@ async def _recv_(self):  # pragma: no cover
             result = None
         return result
 
-    def callback_data(self, data: bytes, addr: tuple = ()) -> int:
+    def callback_data(self, data: bytes, addr: tuple | None = ()) -> int:
         """Handle received data."""
         if addr != ():
             self.receive_queue.put_nowait((data, addr))
diff --git a/pymodbus/transport/transport.py b/pymodbus/transport/transport.py
index 98024702c..51fd99e81 100644
--- a/pymodbus/transport/transport.py
+++ b/pymodbus/transport/transport.py
@@ -159,14 +159,18 @@ def __init__(
         self.transport: asyncio.BaseTransport = None
         self.loop: asyncio.AbstractEventLoop = None
         self.recv_buffer: bytes = b""
-        self.call_create: Callable[[], Coroutine[Any, Any, Any]] = lambda: None
+
+        async def _noop():
+            ...
+
+        self.call_create: Callable[[], Coroutine[Any, Any, Any]] = _noop
         if self.is_server:
             self.active_connections: dict[str, ModbusProtocol] = {}
         else:
-            self.listener: ModbusProtocol = None
+            self.listener: ModbusProtocol | None = None
             self.unique_id: str = str(id(self))
-            self.reconnect_task: asyncio.Task = None
-            self.reconnect_delay_current: float = 0.0
+            self.reconnect_task: asyncio.Task | None = None
+            self.reconnect_delay_current = 0.0
             self.sent_buffer: bytes = b""
 
         # ModbusProtocol specific setup
@@ -313,7 +317,7 @@ def data_received(self, data: bytes) -> None:
         """
         self.datagram_received(data, None)
 
-    def datagram_received(self, data: bytes, addr: tuple) -> None:
+    def datagram_received(self, data: bytes, addr: tuple | None) -> None:
         """Receive datagram (UDP connections)."""
         if self.comm_params.handle_local_echo and self.sent_buffer:
             if data.startswith(self.sent_buffer):
@@ -378,7 +382,7 @@ def callback_disconnected(self, exc: Exception | None) -> None:
         """Call when connection is lost."""
         Log.debug("callback_disconnected called: {}", exc)
 
-    def callback_data(self, data: bytes, addr: tuple = None) -> int:
+    def callback_data(self, data: bytes, addr: tuple | None = None) -> int:
         """Handle received data."""
         Log.debug("callback_data called: {} addr={}", data, ":hex", addr)
         return 0
@@ -386,7 +390,7 @@ def callback_data(self, data: bytes, addr: tuple = None) -> int:
     # ----------------------------------- #
     # Helper methods for external classes #
     # ----------------------------------- #
-    def transport_send(self, data: bytes, addr: tuple = None) -> None:
+    def transport_send(self, data: bytes, addr: tuple | None = None) -> None:
         """Send request.
 
         :param data: non-empty bytes object with data to send.
@@ -514,14 +518,14 @@ class NullModem(asyncio.DatagramTransport, asyncio.Transport):
     listeners: dict[int, ModbusProtocol] = {}
     connections: dict[NullModem, int] = {}
 
-    def __init__(self, protocol: ModbusProtocol, listen: int = None) -> None:
+    def __init__(self, protocol: ModbusProtocol, listen: int | None = None) -> None:
         """Create half part of null modem"""
         asyncio.DatagramTransport.__init__(self)
         asyncio.Transport.__init__(self)
         self.protocol: ModbusProtocol = protocol
         self.other_modem: NullModem = None
         self.listen = listen
-        self.manipulator: Callable[[bytes], list[bytes]] = None
+        self.manipulator: Callable[[bytes], list[bytes]] | None = None
         self._is_closing = False
 
     # -------------------------- #
@@ -631,7 +635,9 @@ def get_write_buffer_limits(self) -> tuple[int, int]:
         """Set flush limits"""
         return (1, 1024)
 
-    def set_write_buffer_limits(self, high: int = None, low: int = None) -> None:
+    def set_write_buffer_limits(
+        self, high: int | None = None, low: int | None = None
+    ) -> None:
         """Set flush limits"""
 
     def write_eof(self) -> None:
diff --git a/pymodbus/transport/transport_serial.py b/pymodbus/transport/transport_serial.py
index 9e26114ca..277b3f7f6 100644
--- a/pymodbus/transport/transport_serial.py
+++ b/pymodbus/transport/transport_serial.py
@@ -22,7 +22,7 @@ def __init__(self, loop, protocol, *args, **kwargs) -> None:
         self._protocol: asyncio.BaseProtocol = protocol
         self.sync_serial = serial.serial_for_url(*args, **kwargs)
         self._write_buffer: list[bytes] = []
-        self.poll_task = None
+        self.poll_task: asyncio.Task | None = None
         self._poll_wait_time = 0.0005
         self.sync_serial.timeout = 0
         self.sync_serial.write_timeout = 0
@@ -35,7 +35,7 @@ def setup(self):
             self.async_loop.add_reader(self.sync_serial.fileno(), self._read_ready)
         self.async_loop.call_soon(self._protocol.connection_made, self)
 
-    def close(self, exc=None):
+    def close(self, exc: Exception | None = None) -> None:
         """Close the transport gracefully."""
         if not self.sync_serial:
             return
@@ -115,7 +115,7 @@ def is_closing(self):
         """Return True if the transport is closing or closed."""
         return False
 
-    def abort(self):
+    def abort(self) -> None:
         """Close the transport immediately."""
         self.close()