anchor.diff:    final RawServerSocket _socket;
     late StreamController<RawSecureSocket> _controller;
     StreamSubscription<RawSocket>? _subscription;
  -  final SecurityContext _context;
  +  final SecurityContext? _context;
     final bool requestClientCertificate;
     final bool requireClientCertificate;
     final List<String>? supportedProtocols;
  
positive.code:    * multiple isolates this way.
     */
    static Future<RawSecureServerSocket> bind(
        address, int port, SecurityContext context,
        {int backlog: 0,
        bool v6Only: false,
        bool requestClientCertificate: false,
  
negative.code:    * isolates this way.
     */
    static Future<SecureServerSocket> bind(
        address, int port, SecurityContext? context,
        {int backlog: 0,
        bool v6Only: false,
        bool requestClientCertificate: false,
  