private Set<String> getNestedSet() {
        Set<String> nestSet = nestingTracker.get();
        if (nestSet == null) {
            nestSet = new HashSet<>();
            nestingTracker.set(nestSet);
        }
        return nestSet;
    }
removes the mark set by call to checkAndAddNested (if any was set)
main/src/main/java/cgeo/geocaching/filters/core/NamedFilterGeocacheFilter.java