fixed json formatting

WatcherAgent/src/main.rs

@@ -114,10 +114,11 @@ async fn main() -> Result<(), Box<dyn Error + Send + Sync>> {
     let container_dto = if let Some(ref docker_manager) = docker_manager {
         docker_manager.create_registration_dto().await?
     } else {
+        println!("Fallback for failing registration");
         models::DockerRegistrationDto {
             server_id: 0,
             //container_count: 0, --- IGNORE ---
-            containers: Vec::new(),
+            containers: serde_json::to_value(&"")?,
         }
     };
     let _ =