TYPO3 Core

Every time PHP tries to access an index of an array, which is not set, or a variable that is not defined PHP generated an E_NOTICE and uses NULL as resulting value.

This is bad because of three major reasons:
1. Bugs resulting from an invalid evaluation of the value are very hard to find.
2. You can not trust the type of the variable so you have to check it anywhere you use it.
3. Not checking keys is considered bad code.

And a lot of other (major and minor) reasons to check the key/variable before accessing it, including tiny performance improvements as a positive side effect.

Mission:¶

Always check if the variable/key exists before accessing it.
If the value is not existent use the expected default value (e.g.: empty string, zero, null..)

How to work on this:¶

Edit UnitTests.xml in core/Build and set convertNoticesToExceptions="true" and stopOnFailure="true" as <phpunit> tag attributes.
Go to \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::initializeBasicErrorReporting and set error_reporting(E_ALL)
Run all unit tests. PHPUnit will halt on the first error.

Create a child issue on this ticket that combines some changes into logic units.
There shouldn't be more than 20 changes per patch to keep them simple and increase velocity. Smaller patches are getting approved and merged faster.