query builder HAVING clause

Hello!
I'm trying to write SQL with query builder(QB). I want to use HAVING clause with MIN() function in it. In Mysql CLI everything works fine, but QB produce string with "IS NULL" in the end.

$this->db->HAVING('MIN(sp.s_price)', null, false);
$this->db->HAVING('MIN(sp.s_price)', '', false);
It's didn't help.

Code:

SELECT `s`.`s_code`, `sp`.`s_price`
FROM `services` `s`
LEFT JOIN `service_prices` `sp` ON `s`.`s_id` = `sp`.`s_id`
WHERE `s`.`s_name` LIKE '%q%' ESCAPE '!'
AND `s`.`s_activity` = '1'
GROUP BY `s`.`s_id`
HAVING MIN(sp.s_price) IS NULL

PHP Code:

$srvcCode = 'q';
$this->db->select('s.s_code, sp.s_price');
$this->db->from('services s');
$this->db->join('service_prices sp', 's.s_id = sp.s_id', 'left');
$this->db->like('s.s_name', $srvcCode);
$this->db->where('s.s_activity', '1');
$this->db->group_by('s.s_id');
$this->db->having('MIN(sp.s_price)');

echo '<pre>';
print_r($this->db->get_compiled_select());
echo '</pre>';
die; 


 
I found workaround $this->db->having("MIN(sp.s_price)", "MIN(sp.s_price)", false);
But It's not a good practice.

Is it a bug or I didn't understand something?

English isn’t my first language, so please excuse any mistakes 

Hello!
I'm trying to write SQL with query builder(QB). I want to use HAVING clause with MIN() function in it. In Mysql CLI everything works fine, but QB produce string with "IS NULL" in the end.

$this->db->HAVING('MIN(sp.s_price)', null, false);
$this->db->HAVING('MIN(sp.s_price)', '', false);
It's didn't help.

Code:

SELECT `s`.`s_code`, `sp`.`s_price`
FROM `services` `s`
LEFT JOIN `service_prices` `sp` ON `s`.`s_id` = `sp`.`s_id`
WHERE `s`.`s_name` LIKE '%q%' ESCAPE '!'
AND `s`.`s_activity` = '1'
GROUP BY `s`.`s_id`
HAVING MIN(sp.s_price) IS NULL

PHP Code:

$srvcCode = 'q';
$this->db->select('s.s_code, sp.s_price');
$this->db->from('services s');
$this->db->join('service_prices sp', 's.s_id = sp.s_id', 'left');
$this->db->like('s.s_name', $srvcCode);
$this->db->where('s.s_activity', '1');
$this->db->group_by('s.s_id');
$this->db->having('MIN(sp.s_price)');

echo '<pre>';
print_r($this->db->get_compiled_select());
echo '</pre>';
die; 


 
I found workaround $this->db->having("MIN(sp.s_price)", "MIN(sp.s_price)", false);
But It's not a good practice.

Is it a bug or I didn't understand something?

English isn’t my first language, so please excuse any mistakes 

Your HAVING clause missed an operator. That's why Query Builder issues an IS NULL for it.
You can read about SQL HAVING here and QB having() here