branch : master , version : 2.7.0-SNAPSHOT
ServiceConfig#doExportUrlsFor1Protocol , line 482

<img width="890" alt="image" src="https://user-images.githubusercontent.com/6971152/41273922-035827c2-6e4e-11e8-8a72-71562d138cf9.png">

The type of Constant.SCOPE_Xxx is String already , no need to call toString() again
private void checkRef() {
        
        if (ref == null) {
            throw new IllegalStateException("ref not allow null!");
        }
        if (!interfaceClass.isInstance(ref)) {
            throw new IllegalStateException("The class "
                    + ref.getClass().getName() + " unimplemented interface "
                    + interfaceClass + "!");
        }
    }
    public synchronized void unexport() {
        if (!exported) {
            return;
        }
        if (unexported) {
            return;
        }
        if (!exporters.isEmpty()) {
            for (Exporter<?> exporter : exporters) {
                try {
                    exporter.unexport();
                } catch (Throwable t) {
                    logger.warn("unexpected err when unexport" + exporter, t);
                }
            }
            exporters.clear();
        }
        unexported = true;
    }