public Boolean getValue() {
        String value = input.getDomProperty("value");
        if ("0".equals(value)) {
            return null;
        }
        else if ("1".equals(value)) {
            return Boolean.TRUE;
        }
        else if ("2".equals(value)) {
            return Boolean.FALSE;
        }
        throw new IllegalStateException();
    }
Component wrapper for the PrimeFaces {@code p:triStateCheckbox}.
primefaces-selenium/primefaces-selenium-components/src/main/java/org/primefaces/selenium/component/TriStateCheckbox.java