unreachable variable for groovy script

    public class ConfigurationDB {
    public static final instance = new ConfigurationDB ();
     
    def String url
    def String server
    def String port
    def String database
    def String user
    def String password
     
    static getInstance() {
    return instance;
    }
     
    public ConfigurationDB () {
     
    this.server = "localhost";
    this.port = "5432";
    this.database = "db";
    this.user = "user";
    this.password = "pass";
    this.url = "jdbc:postgresql://"+this.server+":"+this.port+"/"+this.database;
    }
    }

    Tipo de Expresion no admitido para la prueba:
    Parametro de entrada script esta usando una expresion que contiene una referencia inalcanzable.
     
    Type of expression unadmitted for the test:
    Imput Parameter 'script' is using a expression that contain a unreachable variable.