Missing utf8_encode with php7

[isawien45]

2018/08/28 12:36:42 [error] 15425#15425: *2780 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Call to undefined function utf8_encode() in /var/www/ampache/lib/vendor/szymach/c-pchart/src/Resources/data/constants.php:50
Stack trace:
#0 /var/www/ampache/lib/vendor/composer/autoload_real.php(70): require()
#1 /var/www/ampache/lib/vendor/composer/autoload_real.php(60): composerRequirec36a7139a26d39786825cfccbcf1a636('6dcc7fc69104725...', '/var/www/ampach...')
#2 /var/www/ampache/lib/vendor/autoload.php(7): ComposerAutoloaderInitc36a7139a26d39786825cfccbcf1a636::getLoader()
#3 /var/www/ampache/lib/init-tiny.php(57): require_once('/var/www/ampach...')
#4 /var/www/ampache/lib/init.php(29): require_once('/var/www/ampach...')
#5 /var/www/ampache/index.php(23): require_once('/var/www/ampach...')
#6 {main}

Debian 9 with yunohost 3.1.

I have fixed this on my instance with installing lib php7.0-xml
But maybe to add to install script ?