@Override
    public Cost getDefaultCost() {
        if (notCollectionExecutor.getDefaultCost() == Cost.EXHAUSTIVE) {
            return Cost.EXHAUSTIVE;
        } else {
            return Cost.MULTI_RETURN_INDEX_MATCHING;
        }
    }
Implementation of {@link CollectionExecutor} which handles not condition.
modules/siddhi-core/src/main/java/io/siddhi/core/util/collection/executor/NotCollectionExecutor.java