[TASK] Remove the first few E_NOTICEs occuring in the unit tests

PHP throws E_NOTICE when not existing array keys are accessed.
The received value will become null.

This patch aims to reduce the number of generated notices,
to increase readability and reliability of the changed methods.

Resolves: #70587
Related: #70584
Releases: master
Change-Id: I23ee39b0d89f1be828565cbe6c745b6eeefdcfde
Reviewed-on: https://review.typo3.org/43988


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>