private function add(Writer $writer, array $properties)
    {
        foreach ($properties as $property) {
            if (! is_null($this->$property)) {
                $writer->write([$property => $this->$property]);
            }
        }
    }
private function add(Writer $writer, array $properties)
    {
        foreach ($properties as $property) {
            if (! is_null($this->$property)) {
                $writer->write([$property => $this->$property]);
            }
        }
    }
private function add ( Writer $ writer , array $ properties ) { foreach ( $ properties as $ property ) { if ( ! is_null ( $ this -> $ property ) ) { $ writer -> write ( [ $ property => $ this -> $ property ] ) ; } } }
Adds property from properties to url if it is not null.

@param Writer $writer
@param array $properties
Adds property from properties to url if it is not null .