IEF fills entity in DefaultSelection

Problem/Motivation

When creating and using a Plugin\EntityReferenceSelection\DefaultSelection entity reference selector, one is supposed to receive the entity of the form in $this->configuration['entity']. Not the case with IEF, it always returns NULL (both new and existing entities).

Steps to reproduce

- a custom entity referencing another
- said entity using a handler
- said handler trying to read $this->configuration['entity']
- said entity being NULL

Proposed resolution

- passing or not killing the entity