Ignore empty payloads from DSMR Reader (#86841)

* Ignore empty payloads from DSMR Reader

* Simplify empty payload handling

If the native value hasn't changed, requesting to store it won't have a performance impact.

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

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Co-authored-by: Franck Nijhof <frenck@frenck.nl>

homeassistant/components/dsmr_reader/sensor.py

@@ -69,7 +69,10 @@ class DSMRSensor(SensorEntity):
         @callback
         def message_received(message):
             """Handle new MQTT messages."""
-            if self.entity_description.state is not None:
+            if message.payload == "":
+                self._attr_native_value = None
+            elif self.entity_description.state is not None:
+                # Perform optional additional parsing
                 self._attr_native_value = self.entity_description.state(message.payload)
             else:
                 self._attr_native_value = message.payload