public Expression getReducedExpression() {
        Object pop = this.conditionOperands.pop();
        if (pop instanceof String) {
            return Expression.value(true);
        }
        return ((Expression) pop);
    }
Visitor class to reduce on condition Expression
modules/siddhi-core/src/main/java/io/siddhi/core/aggregation/AggregationExpressionVisitor.java