@Override
    public String execute(SampleResult previousResult, Sampler currentSampler) throws InvalidVariableException {
        String originalString = values[0].execute();
        String mode = null; // default
        if (values.length > 1) {
            mode = values[1].execute();
        }
        if(StringUtils.isEmpty(mode)){
            mode = ChangeCaseMode.UPPER.getName(); // default
        }
        String targetString = changeCase(originalString, mode);
        addVariableValue(targetString, values, 2);
        return targetString;
    }
@Test
    public void testEmptyMode() throws Exception {
        String returnValue = execute("ab-CD eF", "");
        assertEquals("AB-CD EF", returnValue);
    }