quic: do not log empty cyu array

Ticket: #5167

rust/src/quic/logger.rs

@@ -30,6 +30,7 @@ fn log_template(tx: &QuicTransaction, js: &mut JsonBuilder) -> Result<(), JsonEr
             js.set_string("ua", &String::from_utf8_lossy(&ua))?;
         }
     }
+    if tx.cyu.len() > 0 {
         js.open_array("cyu")?;
         for cyu in &tx.cyu {
             js.start_object()?;
@@ -38,6 +39,7 @@ fn log_template(tx: &QuicTransaction, js: &mut JsonBuilder) -> Result<(), JsonEr
             js.close()?;
         }
         js.close()?;
+    }
 
     js.close()?;
     Ok(())