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可以看到按照图片顺序，properties中设置default属性，在我从configManager中打印的2个注册中心default值都为null,dubbo版本是3.0.12
import static org.apache.dubbo.common.constants.RegistryConstants.REGISTRY_CLUSTER_KEY;
import static org.apache.dubbo.common.constants.RemotingConstants.BACKUP_KEY;
import static org.apache.dubbo.common.utils.PojoUtils.updatePropertyIfAbsent;
/**
 * RegistryConfig
 *
 * @export
 */
public class RegistryConfig extends AbstractConfig {
    public static final String NO_AVAILABLE = "N/A";
    private static final long serialVersionUID = 5508512956753757169L;
    /**
     * Register center address
     */
    private String address;
    /**
     * Username to login register center
     */
    private String username;
    /**
     * Password to login register center
     */
    private String password;
    /**
     * Default port for register center
     */
    private Integer port;
    /**
     * Protocol for register center
     */