public static String substVars(String val, PropertyContainer pc1) throws ScanException {
        return substVars(val, pc1, null);
    }
@Disabled
    @Test
    public void defaultExpansionForEmptyVariables() throws JoranException, ScanException {
        String varName = "var"+diff;
        context.putProperty(varName, "");

        String r = OptionHelper.substVars("x ${"+varName+":-def} b", context);
        assertEquals("x def b", r);
    }