@Test
public void ignoreCarbon12() throws Exception {

    IAtomContainer mol  = builder.newAtomContainer();
    IAtom          atom = builder.newAtom();
    atom.setSymbol("C");
    atom.setMassNumber(12);
    mol.addAtom(atom);
    StringWriter sw = new StringWriter();
    try (MDLV2000Writer mdlw = new MDLV2000Writer(sw)) {
        mdlw.getSetting(MDLV2000Writer.OptWriteMajorIsotopes)
            .setSetting("false");
        mdlw.write(mol);
    }
    assertThat(sw.toString(),
               not(containsString("M  ISO  1   1  12")));
}