diff --git a/src/main/kotlin/org/opensearch/commons/alerting/model/Alert.kt b/src/main/kotlin/org/opensearch/commons/alerting/model/Alert.kt
index 3a3a21e4..e4979407 100644
--- a/src/main/kotlin/org/opensearch/commons/alerting/model/Alert.kt
+++ b/src/main/kotlin/org/opensearch/commons/alerting/model/Alert.kt
@@ -363,7 +363,7 @@ data class Alert(
         }
         out.writeOptionalString(executionId)
         out.writeStringCollection(associatedAlertIds)
-        if (!clusters.isNullOrEmpty()) out.writeStringArray(clusters.toTypedArray())
+        out.writeOptionalStringArray(clusters?.toTypedArray())
     }
 
     companion object {