code: public FilteredForestConfiguration withBlackList(String... hostNames) {
      if ( whiteList.size() > 0 ) throw new IllegalStateException("whiteList already initialized");
      if ( hostNames == null ) throw new IllegalArgumentException("hostNames must not be null");
      for ( String hostName : hostNames ) {
        if ( hostName != null ) blackList.add(hostName.toLowerCase());
      }
      return this;
    }
docs: Add hosts to the list of black-listed hosts (hosts which the Batcher will not see when it
  calls listForests).  Do not use at the same time as withWhiteList.
  
  @param hostNames the hosts to black-list
  @return this instance (for method chaining)