public boolean toStream() {
        return metaStreamEvent.getEventType() == MetaStreamEvent.EventType.DEFAULT ||
                metaStreamEvent.getEventType() == MetaStreamEvent.EventType.WINDOW;
    }
Parent implementation for all process stream receivers(Multi/Single/State). Any newly written process stream
receivers should extend this. ProcessStreamReceivers are the entry point to Siddhi queries.
modules/siddhi-core/src/main/java/io/siddhi/core/query/input/ProcessStreamReceiver.java