diff --git a/Source/MQTTnet/Server/InjectedMqttApplicationMessage.cs b/Source/MQTTnet/Server/InjectedMqttApplicationMessage.cs
index 90406134..0190ec00 100644
--- a/Source/MQTTnet/Server/InjectedMqttApplicationMessage.cs
+++ b/Source/MQTTnet/Server/InjectedMqttApplicationMessage.cs
@@ -13,8 +13,8 @@ namespace MQTTnet.Server
         {
             ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
         }
-        
-        public string SenderClientId { get; set; }
+
+        public string SenderClientId { get; set; } = string.Empty;
 
         public MqttApplicationMessage ApplicationMessage { get; set; }
     }