src/java.base/share/classes/sun/net/ftp/FtpProtocolException.java

@@ -30,10 +30,11 @@
  * that a command isn't supported.
  * <p>The specific error code can be retreived with {@link #getReplyCode() }.</p>
  * @author      Jonathan Payne
  */
 public class FtpProtocolException extends Exception {
+    @java.io.Serial
     private static final long serialVersionUID = 5978077070276545054L;
     private final FtpReplyCode code;
 
     /**
      * Constructs a new {@code FtpProtocolException} from the