codeigniter email attach will cause error or will proceed to send email if the value incorrect?

public function send_email(){
        $email_from     = $this->input->post('email_from');
        $email_fromname = $this->input->post('email_fname');
        $email_to       = $this->input->post('email_to');
        $subject        = $this->input->post('subject');
        $message        = $this->input->post('message');

        if($this->input->post('file_name') !== NULL){
            $file_name      = base_url('upload/ext_policy/policy/'.$this->input->post('file_name'));
        }else{
            $file_name      = '-';
        }

        if($this->input->post('file_name2') !== NULL){
            $file_name2     = base_url('upload/ext_policy/attach/'.$this->input->post('file_name2'));
        }else{
            $file_name2     = '-';
        }

        if($this->input->post('file_name3') !== NULL){
            $file_name3     = base_url('upload/ext_policy/reportform/'.$this->input->post('file_name3'));
        }else{
            $file_name3     = '-';
        }

        // $file_name      = base_url('upload/ext_policy/policy/'.$this->input->post('file_name'));
        // $file_name2     = base_url('upload/ext_policy/attach/'.$this->input->post('file_name2'));
        // $file_name3     = base_url('upload/ext_policy/reportform/'.$this->input->post('file_name3'));

        $config =   array(
            'mailtype'      => 'html',
            'charset'       => 'utf-8',
            'protocol'      => 'smtp',
            'smtp_host'     => 'xxx.xx.xxx.xx',
            'smtp_user'     => '',
            'smtp_pass'     => '',
            'smtp_port'     => '25'
        );

        $this->load->library('email',$config);
        $this->email->set_newline("\r\n");
        $this->email->from($email_from, $email_fromname);
        $this->email->to($email_to);
        $this->email->subject($subject);
        $this->email->message($message);
        $this->email->attach($file_name);
        $this->email->attach($file_name2);
        $this->email->attach($file_name3);
        $emailsent  = $this->email->send();

        if($emailsent == TRUE){
            return TRUE;
        }else{
            return $this->email->print_debugger();
        }
    }

I've scenarios that only send one or two of the 3 files that I've uploaded. but in another scenario, I've to send all 3 files.

my question is Can Codeigniter send an email if one or two of 3 attach method's value set to something(string "-")? will Codeigniter continue sending emails without attaching files? or will Codeigniter error and will not send the whole email?

please, if you know about this help me I can't find the answer on google...

I've tested that code works perfectly on another scenario that I always attach 1 file with the correct path.