code: public static boolean isUnsupported(SocketAddress remoteAddress, SessionProtocol protocol) {
          final String key = key(remoteAddress);
          final CacheEntry e;
          final long stamp = lock.readLock();
          try {
              e = cache.get(key);
          } finally {
              lock.unlockRead(stamp);
          }
  
          if (e == null) {
              // Can't tell if it's unsupported
              return false;
          }
  
          return e.isUnsupported(protocol);
      }
docs: Returns {@code true} if the specified {@code remoteAddress} is known to have no support for
  the specified {@link SessionProtocol}.