code: @SuppressWarnings("unchecked")
      static <S extends Storable> PropertyFilter<S> getCanonical(PropertyFilter<S> filter,
                                                                 int bindID)
      {
          if (filter.mBindID == bindID) {
              return filter;
          }
          return (PropertyFilter<S>) cCanonical
              .put(new PropertyFilter<S>(filter.getChainedProperty(),
                                         filter.getOperator(), bindID, filter.mConstant));
      }
docs: Returns a canonical instance, creating a new one if there isn't one
  already in the cache.