private static RouteTableException reject(final byte[] relatedKey, final String message) {
        return new RouteTableException("key: " + BytesUtil.toHex(relatedKey) + ", message: " + message);
    }
Returns the startKey of next region.
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/client/RegionRouteTable.java