Problem while installing : Error while resoliving diagnostics.optionnal

Hi!

just installed 3.0.2. (fresh install, no upgrade).
Navigated to [root]/analytics/index.php and started install (“next” button).
I get the following :

Error while resolving diagnostics.optional[14]. No entry or class found for ‘Piwik\Plugins\CustomPiwikJs\Diagnostic\PiwikJsCheck’

What should I do ?

Thanks