Add default value for rs485-settings in class Serial init

Since this class might use for other python script directly. Add default value to prevent init failed while calling by other python script

Author: rickwu666666

contrib/checkbox-ce-oem/checkbox-provider-ce-oem/bin/serial_test.py

@@ -75,7 +75,12 @@ def __init__(
         self.stopbits = stopbits
         self.timeout = timeout
         self.data_size = data_size
-        self.rs485_settings = rs485_settings
+        self.rs485_settings = rs485_settings or {
+            "rts_level_for_tx": False,  # Default to False
+            "rts_level_for_rx": False,  # Default to False
+            "delay_before_tx": 0.0,  # Default to 0.0
+            "delay_before_rx": 0.0,  # Default to 0.0
+        }
         self.ser = self.serial_init(node)
         self.group = []
         for ser in group: