public function set( $key, $value ) {

		/**
		 * Using `isset()` allows us to explicitly save a value of `false`
		 * since the `get()` method will return the default value `false` making it look
		 * as if the value hasn't changed (when it actually has).
		 */
		if ( ! isset( $this->$key ) || $value !== $this->get( $key ) ) {
			$this->data[ sanitize_key( $key ) ] = maybe_serialize( $value );
			$this->is_clean                     = false;
		}

		return $this->get( $key );

	}