@Override
    public boolean contains(StateEvent matchingEvent, Object storeEvents) {
        try {
            for (StreamEvent storeEvent : (Collection<StreamEvent>) storeEvents) {
                matchingEvent.setEvent(storeEventPosition, storeEvent);
                if ((Boolean) expressionExecutor.execute(matchingEvent)) {
                    return true;
                }
            }
            return false;
        } finally {
            matchingEvent.setEvent(storeEventPosition, null);
        }
    }
Operator which is related to non-indexed In-memory table operations.
modules/siddhi-core/src/main/java/io/siddhi/core/util/collection/operator/CollectionOperator.java