private static String getTimeZone(SiddhiAppContext siddhiAppContext) {
        String timeZone = siddhiAppContext.getSiddhiContext().getConfigManager().extractProperty(SiddhiConstants
                .AGG_TIME_ZONE);
        if (timeZone == null) {
            return SiddhiConstants.AGG_TIME_ZONE_DEFAULT;
        }
        return timeZone;
    }
This is the parser class of incremental aggregation definition.
modules/siddhi-core/src/main/java/io/siddhi/core/util/parser/AggregationParser.java