php - CodeIgniter form validation rule won't run if string is empty -

i have custom rule, regex[table_name.column_name.post_value], using in following manner:

$this->form_validation->set_rules(   'postal_code',   'postal code',   'regex[countries.postal_code_regex.country_code]' ); 

and here custom rule's function in my_form_validation.php:

public function regex($str, $field){     list($table, $col, $post_val)=explode('.', $field);     // grab regex     $regex = $this->ci  ->db                         ->limit(1)                         ->select($col)                         ->where($post_val, $_post[$post_val])                         ->get($table)                         ->row($col);      return preg_match('/'.$regex.'/', $str) === 1; } 

how codeigniter run rule if user sends empty string?

note: cannot use required rule depends on whether database has regex or not.

try below code:

public function regex($str, $field){     list($table, $col, $post_val)=explode('.', $field);     // grab regex     $regex = $this->ci  ->db                         ->limit(1)                         ->select($col)                         ->where($post_val, $_post[$post_val])                         ->get($table)                         ->row($col);      if(trim($str) === "")     $str = 1;     return preg_match('/'.$regex.'/', $str) === 1; }