code: public PumpStreamHandler pumps() {
      if (streams == null)
        return null;
      if (!(streams instanceof PumpStreamHandler))
        throw new IllegalStateException("Only PumpStreamHandler is supported.");
      return (PumpStreamHandler) streams;
    }
docs: @return current PumpStreamHandler (maybe <code>null</code>).
  @throws IllegalStateException if the current stream handler is not an instance of {@link PumpStreamHandler}.
  
  @see #streams()