Problem/Motivation
As in title.
Steps to reproduce
Create a view with no relationships on Master, add a display with a relationship (override Master), add a numeric filter using the relationship with "empty" or "not empty" operator.
Proposed resolution
Looks like the problem is in Drupal\views\Plugin\views\filter\FilterPluginBase::init(), when determining if empty operators are allowed. Looks like it checks if master has relationships, while it should check the current display instead.