code: private function htmlAttributesCallback($name, $value)
      {
          if (false === $value || null === $value) {
              return '';
          }
  
          return ' '.$this->renderHtmlAttribute($name, $value);
      }
docs: Prepares an attribute key and value for HTML representation.
  
  It removes empty attributes.
  
  @param string $name  The attribute name
  @param string $value The attribute value
  
  @return string The HTML representation of the HTML key attribute pair.