public BigDecimal getAsDecimal(final int idx, final BigDecimal defaultValue) {
        return isValidIdx(idx) && list.get(idx).isNumeric() ? list.get(idx).getAsDecimal() : defaultValue;
    }
Encapsulates a list of {@link cgeo.geocaching.utils.formulas.Value}'s for handling as parameter lists in {@link Formula}
main/src/main/java/cgeo/geocaching/utils/formulas/ValueList.java