class RequestValidator {

    public static void validateExpression(Expression expression) {
        Assert.notNull(expression, "subscription expression can't null");
        //Only AND operator is supported now
        Assert.isTrue(Operator.AND.equals(expression.getOperator()), "Only AND operator is supported now");
        Assert.notEmpty(expression.getOperands(), "Operands can't be empty");
        expression.getOperands().forEach(operand -> validateOperand(operand));
    }

}