Trait variables are accessed in a way that isn't null-safe

[KorvinSzanto]

The problem is we don't have either:

• A way to guarantee that $this->output is not null
• The ability to use PHP 8 null safe operator like $this-output?->foo()

so ideally if we wanted this to be type safe we'd use getter methods on traits to access variables in a way that guarantees an object is returned and not null.

Originally posted by @KorvinSzanto in #22 (comment)