Ensure tesla_wall_connector config flow title_placeholders items are [str, str] (#127208)

homeassistant/components/tesla_wall_connector/config_flow.py

@@ -46,7 +46,6 @@ class TeslaWallConnectorConfigFlow(ConfigFlow, domain=DOMAIN):
         """Initialize config flow."""
         super().__init__()
         self.ip_address: str | None = None
-        self.serial_number = None
 
     async def async_step_dhcp(
         self, discovery_info: dhcp.DhcpServiceInfo
@@ -70,23 +69,21 @@ class TeslaWallConnectorConfigFlow(ConfigFlow, domain=DOMAIN):
             )
             return self.async_abort(reason="cannot_connect")
 
-        self.serial_number = version.serial_number
+        serial_number: str = version.serial_number
 
-        await self.async_set_unique_id(self.serial_number)
+        await self.async_set_unique_id(serial_number)
         self._abort_if_unique_id_configured(updates={CONF_HOST: self.ip_address})
 
         _LOGGER.debug(
             "No entry found for wall connector with IP %s. Serial nr: %s",
             self.ip_address,
-            self.serial_number,
+            serial_number,
         )
 
-        placeholders = {
+        self.context["title_placeholders"] = {
             CONF_HOST: self.ip_address,
-            WALLCONNECTOR_SERIAL_NUMBER: self.serial_number,
+            WALLCONNECTOR_SERIAL_NUMBER: serial_number,
         }
-
-        self.context["title_placeholders"] = placeholders
         return await self.async_step_user()
 
     async def async_step_user(