public boolean filter(final Geocache cache) {
        if (tree == null) {
            return true;
        }
        final Boolean result = tree.filter(cache);
        return result == null ? this.includeInconclusive : result;
    }
returns true if this filter and other filter would filter same results
main/src/main/java/cgeo/geocaching/filters/core/GeocacheFilter.java