protected function getHeaderText() {
        
        $headers = [];
        
        // go through the column definitions
        for ($i=0; $i<count($this->columnDefinitions); ++$i) {
            
            $next = $this->columnDefinitions[$i];

            // if one column has header text
            if ($this->columnDefinitions[$i]->hasHeaderText()) {

                // then there is a header
                $headers[] = $next->getHeaderText();
            
            // there is no header
            } else {
                
                // put in a blank placeholder
                $headers[] = "";
            }
        }

        // none of the columns had header text
        return $headers;       
    }