OpenLayers filter on null and 0

I have this filter:

var filter_unset = new OpenLayers.Filter.Comparison({
        type: OpenLayers.Filter.Comparison.EQUAL_TO,
        property: attribute,

        value: 0
 });

Now, I want the filter to apply on null values as well, something like:

        value: 0 or NULL  

Can I do this?