code: public static Version getServerVersion(Channel channel) {
      Version version = channel.attr(SERVER_VERSION).get();
      if (version == null) {
        throw new IllegalStateException("Server version attribute not yet set by "
            + DcpConnectHandler.class.getSimpleName());
      }
      return version;
    }
docs: Returns the Couchbase Server version associated with the given channel.
  
  @throws IllegalStateException if {@link DcpConnectHandler} has not yet issued
  a Version request and processed the result.