diff --git a/pymodbus/transport/transport.py b/pymodbus/transport/transport.py
index 9339bdcd5..747ccc089 100644
--- a/pymodbus/transport/transport.py
+++ b/pymodbus/transport/transport.py
@@ -159,7 +159,7 @@ 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
+        self.call_create: Callable[[], Coroutine[Any, Any, Any]] = lambda: None  # type: ignore[assignment]
         if self.is_server:
             self.active_connections: dict[str, ModbusProtocol] = {}
         else:
@@ -517,7 +517,7 @@ def __init__(self, protocol: ModbusProtocol, listen: int | None = None) -> None:
         asyncio.DatagramTransport.__init__(self)
         asyncio.Transport.__init__(self)
         self.protocol: ModbusProtocol = protocol
-        self.other_modem: NullModem = None
+        self.other_modem: NullModem
         self.listen = listen
         self.manipulator: Callable[[bytes], list[bytes]] | None = None
         self._is_closing = False
@@ -590,10 +590,10 @@ def close(self) -> None:
         if self.connections:
             with suppress(KeyError):
                 del self.connections[self]
-        if self.other_modem:
-            self.other_modem.other_modem = None
+        if hasattr(self, 'other_modem'):
+            del self.other_modem.other_modem
             self.other_modem.close()
-            self.other_modem = None
+            del self.other_modem
         if self.protocol:
             self.protocol.connection_lost(None)
 
diff --git a/pymodbus/transport/transport_serial.py b/pymodbus/transport/transport_serial.py
index 63c1affa5..730f9f7fe 100644
--- a/pymodbus/transport/transport_serial.py
+++ b/pymodbus/transport/transport_serial.py
@@ -38,7 +38,7 @@ def setup(self):
 
     def close(self, exc: Exception | None = None) -> None:
         """Close the transport gracefully."""
-        if not self.sync_serial:
+        if not hasattr(self, 'sync_serial'):
             return
         with contextlib.suppress(Exception):
             self.sync_serial.flush()
@@ -51,7 +51,7 @@ def close(self, exc: Exception | None = None) -> None:
         else:
             self.async_loop.remove_reader(self.sync_serial.fileno())
         self.sync_serial.close()
-        self.sync_serial = None
+        del self.sync_serial
         if exc:
             with contextlib.suppress(Exception):
                 self._protocol.connection_lost(exc)