Zipoutputstream e objectoutputstream

Cripto c = new Cripto();
                              ZipOutputStream zs = new ZipOutputStream(ostream);//objectoutputstream
                              byte[] by = c.serializar(getListaDoSus());
                              System.out.println("Tamanho do envio: "+by.length);
                              zs.write(by);

java.util.zip.ZipException: no current ZIP entry

at java.util.zip.ZipOutputStream.write(Unknown Source)

at java.io.FilterOutputStream.write(Unknown Source)

at quiposus.Servidor.run(QuipoSus.java:426)