public function findByUnicode($unicode = null) : string
    {
        if (is_null($unicode)) {
            throw IsNull::create("Please provide a valid UTF-8 Unicode value");
        }

        $emojis = array_flip($this->getEmojis());

        if (! array_key_exists($unicode, $emojis)) {
            throw UnknownUnicode::create($unicode);
        }

        return $emojis[$unicode];
    }