Fix null published for attribute output. https://github.com/Koenkk/zigbee2mqtt/issues/4054

lib/controller.js

@@ -344,7 +344,7 @@ class Controller {
     async iteratePayloadAttributeOutput(topicRoot, payload, options) {
         for (const [key, value] of Object.entries(payload)) {
             let subPayload = value;
-            let message;
+            let message = null;
 
             // Special cases
             if (key === 'color' && utils.objectHasProperties(subPayload, ['r', 'g', 'b'])) {
@@ -362,7 +362,9 @@ class Controller {
                 message = typeof subPayload === 'string' ? subPayload : JSON.stringify(subPayload);
             }
 
-            await this.mqtt.publish(`${topicRoot}${key}`, message, options);
+            if (message !== null) {
+                await this.mqtt.publish(`${topicRoot}${key}`, message, options);
+            }
         }
     }