public void setNextProcessor(OutputRateLimiter outputRateLimiter) {
        if (this.outputRateLimiter == null) {
            this.outputRateLimiter = outputRateLimiter;
        } else {
            throw new SiddhiAppCreationException("outputRateLimiter is already assigned");
        }
    }
Processor implementation representing selector portion of the Siddhi query.
modules/siddhi-core/src/main/java/io/siddhi/core/query/selector/QuerySelector.java