$this->user_id of type null|string is incompatible with the type integer expected by parameter $id of CoffeeCode\DataLayer\DataLayer::findById().
(
Ignorable by Annotation
)
If this is a false-positive, you can also ignore this issue in your code via the ignore-type annotation
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$this->user = (new User())->findById(/** @scrutinizer ignore-type */ $this->user_id)->data();