@Override
    public int hashCode() {

        int result = streamId != null ? streamId.hashCode() : 0;
        result = 31 * result + (streamIndex != null ? streamIndex.hashCode() : 0);
        result = 31 * result + (isInnerStream ? 1 : 0);
        result = 31 * result + (isFaultStream ? 1 : 0);
        result = 31 * result + (expression != null ? expression.hashCode() : 0);
        return result;
    }
Condition {@link Expression} checking whether the event is null
modules/siddhi-query-api/src/main/java/io/siddhi/query/api/expression/condition/IsNull.java