Resolve phpstan issues in 2.0.x

I updated the gitlab-ci file to require phpstan tests pass, so now to fix the phpstan tests.

Can we create a child issues as phpstan having lot of issues reported.
One I can see is Avoid direct drupal calls should be work upon separately
Any thoughts? @damienmckenna

I think there are only a few types of problems identified, just repeated for different classes; I'd prefer to keep it as one issue.

Cool ~~ let me give a try to fix them

Bumping this to 2.0.2.