Raise PHPStan level for the AmpProject\AmpWP package to 4 #4733

Feature description

The plugin package (AmpProject\AmpWP) is currently sitting at and enforcing level 3 of PHPStan static analysis.

There are 27 errors that need to be fixed so that we can raise the level to 4 and enforce this new quality level in Travis CI.

Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

• PHPStan does not show any detected errors when run on level 4.

Implementation brief

• Change the level to 4 in the file phpstan.neon.dist.
• Run composer analyze.
• Fix detected errors until no more are found.

QA testing instructions

Demo

Changelog entry