@Override
    public void endVisitOr() {
        Object rightOperand = this.conditionOperands.pop();
        Object leftOperand = this.conditionOperands.pop();

        boolean isLeftOperandString = leftOperand instanceof String;
        if (isLeftOperandString) {
            if (rightOperand instanceof String) {
                this.conditionOperands.push("true");
            } else {
                this.conditionOperands.push(rightOperand);
            }
        } else {
            if (rightOperand instanceof String) {
                this.conditionOperands.push(leftOperand);
            } else {
                this.conditionOperands.push(
                        Expression.or(
                                ((Expression) leftOperand), ((Expression) rightOperand)
                        )
                );
            }
        }
    }
Visitor class to reduce on condition Expression
modules/siddhi-core/src/main/java/io/siddhi/core/aggregation/AggregationExpressionVisitor.java