public static String substVars(String val, PropertyContainer pc1) throws ScanException {
        return substVars(val, pc1, null);
    }
@Test
    public void defaultValueReferencingAVariable() throws ScanException {
        context.putProperty("v1", "k1");
        String result = OptionHelper.substVars("${undef:-${v1}}", context);
        assertEquals("k1", result);
    }