@Override
    public Attribute.Type getReturnType() {
        return this.returnType;
    }
{@link IncrementalAttributeAggregator} to calculate maximum value based on an event attribute.
modules/siddhi-core/src/main/java/io/siddhi/core/query/selector/attribute/aggregator/incremental/MaxIncrementalAttributeAggregator.java