Added default null to clientmessage

src/dto/message.rs

@@ -6,6 +6,10 @@ use serde_json::Value;
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]
 pub struct ClientMessage {
     pub head: String,
-    #[serde(skip_serializing_if = "Value::is_null")]
+    #[serde(skip_serializing_if = "Value::is_null", default = "null_value")]
     pub body: Value,
 }
+
+fn null_value() -> Value {
+    Value::Null
+}