It seems like $input->getArgument(self::ARGUMENT_USED_FILES) can also be of type string[]; however, parameter $userProvidedPathToConsolidate of AppBundle\ConsolidateUsedFiles\Task::consolidate() does only seem to accept string, 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