Error Message after UPDATE PHP 7 in modules

That is a PHP deprecation notice. It's a valid notice for us, developers, to fix something before the next major release of PHP. However, it's not a real error and not something you need to worry about.

To hide that message, simply go to the Joomla -> Global Configuration area and set "Error Reporting" to "System Level" or "None". That should hide the developer messages like that.

Thanks,
Alex

FYI - I've added this issue to the tracker to address for the next release.