public function initialize_data( $data ) {
		if ( ! $data ) {
			return;
		}

		$this->id       = isset( $data['id'] ) ? $data['id'] : null;
		$this->label    = isset( $data['label'] ) ? $data['label'] : null;
		$this->required = isset( $data['required'] ) ? $data['required'] : null;
		$this->extra    = isset( $data['extra'] ) ? $data['extra'] : null;

		if ( $this->label ) {
			$this->slug = sanitize_title( $this->label );
		}
	}