public List<MetaStateEventAttribute> getOutputDataAttributes() {
        if (outputDataAttributes != null) {
            return outputDataAttributes;
        } else {
            return new ArrayList<MetaStateEventAttribute>();  //return empty arraylist to avoid NPE
        }
    }
Class to hold mapping between StreamEvents and respective StateEvent.
This consist of array of MetaStreamEvents which represent each
StreamEvent within StateEvent
modules/siddhi-core/src/main/java/io/siddhi/core/event/state/MetaStateEvent.java