coordinator: warn when a register converter returns None

The heating season sensor shows as N/A in HA with no indication why.
Add a warning log whenever a register's converter returns None so the
unexpected raw device value is visible in the HA log. This makes the
root cause diagnosable without requiring debug-level logging.

Signed-off-by: Tomáš Hozza <thozza@gmail.com>

Author: thozza

custom_components/atrea_rd5_modbus/coordinator.py

@@ -91,7 +91,16 @@ async def _async_update_data(self) -> dict[str, Any]:
                     raw = result.registers
 
                 for i, key in enumerate(group.keys):
-                    data[key] = REGISTER_MAP[key].convert(raw[i])
+                    converted = REGISTER_MAP[key].convert(raw[i])
+                    if converted is None:
+                        _LOGGER.warning(
+                            "Register %s (addr=%d) returned unexpected raw value %r — "
+                            "converter produced None; entity will be unavailable",
+                            key,
+                            REGISTER_MAP[key].address,
+                            raw[i],
+                        )
+                    data[key] = converted
 
             except Exception as err:
                 _LOGGER.warning(