public static String substVars(String val, PropertyContainer pc1) throws ScanException {
        return substVars(val, pc1, null);
    }
@Test
    public void nestedEmptyVariables() throws ScanException {

        Exception e = assertThrows(Exception.class, () -> {
            OptionHelper.substVars("${${${}}}", context);
        });
        String expectedMessage =  CIRCULAR_VARIABLE_REFERENCE_DETECTED+"${ ?  ? } --> ${ ? } --> ${}]";
        assertEquals(expectedMessage, e.getMessage());
    }