I have to update the php version on our hosting platform from 5.6 to 7.1.
The theme work fine with the 5.6 php version.
But with the 7.2 version the site is unreachable with this error message :
Error :  operator not supported for strings dans md_cortana_links__nav_mainmenu() (line 658 in /home/.../.../themes/md_cortana/theme_setting/front/function.theme.inc).
Thanks for your support.