code: public static <S extends Storable> ClosedFilter<S> getClosedFilter(Class<S> type) {
          SoftValuedCache<Object, Filter<S>> filterCache = getFilterCache(type);
          synchronized (filterCache) {
              Filter<S> filter = filterCache.get(CLOSED_KEY);
              if (filter == null) {
                  filter = ClosedFilter.getCanonical(type);
                  filterCache.put(CLOSED_KEY, filter);
              }
              return (ClosedFilter<S>) filter;
          }
      }
docs: Returns a cached filter instance that operates on the given type, which
  prevents any results from passing through.
  
  @param type type of Storable that query is made against
  @return canonical Filter instance
  @see ClosedFilter