@Override
    public void sinkEvents(int eventBitsToAdd) {
        if (isOrWasAttached()) {
            Event.sinkEvents(inputElem, eventBitsToAdd
                    | Event.getEventsSunk(inputElem));
        } else {
            super.sinkEvents(eventBitsToAdd);
        }
    }
Checks or unchecks the check box, firing {@link ValueChangeEvent} if
appropriate.
<p>
Note that this <em>does not</em> set the value property of the checkbox
input element wrapped by this widget. For access to that property, see
{@link #setFormValue(String)}

@param value      true to check, false to uncheck; null value implies false
@param fireEvents If true, and value has changed, fire a
                  {@link ValueChangeEvent}
stroom-core-client-widget/src/main/java/stroom/widget/tickbox/client/view/CustomCheckBox.java