Problem/Motivation
Like the already committed #2913971: Views regression: 8.4.x EntityField can't handle a null row value from a non-required relationship, there are multiple places where the return value of \Drupal\views\Plugin\views\field\FieldPluginBase::getEntity is not checked for NULL values, leading to WSOD. Setting major thus.
Proposed resolution
Fix all these like in the linked issue. A muscling-through of the 25 occurences i could find is in attached patch.
Remaining tasks
Decide what tests we need and add them.
User interface changes
None.
API changes
Some internal methods' signatures changed from foo to foo|null. Given that the unexpected value null only occurs when until now we got a WSOD, this will not make anything worse for anyone.
* \Drupal\views\Entity\Render\EntityTranslationRenderTrait::getEntityTranslation
* \Drupal\views\Plugin\views\field\LinkBase::getUrlInfo
Data model changes
None.
