It seems like $provider can also be of type null; however, parameter $provider of WBW\Bundle\CoreBundle\Ma...eManager::setProvider() does only seem to accept WBW\Library\Symfony\Prov...\ThemeProviderInterface, maybe add an additional type check?
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Ignorable by Annotation
)
If this is a false-positive, you can also ignore this issue in your code via the ignore-type annotation