@Test public void noNullPointerForStaticIsotopes() throws Exception {

    Isotopes is = Isotopes.getInstance();
    IIsotope carbon = is.getMajorIsotope("C");
    MolecularFormula mf = new MolecularFormula();
    mf.addIsotope(carbon, 10);
    MolecularFormulaManipulator.getNaturalExactMass(mf);
}