Error: Call to a member function addMessage() on null

Problem/Motivation

I am extending the Devel Generate functionality via custom Plugin (which extends DevelGenerateBase) to generate content for Custom Entities. When accessing via Drupal UI (Configuration->Generate->{{CustomOption}}) and try to create content I get:

Error: Call to a member function addMessage() on null in Drupal\devel_generate\DevelGenerateBase->setMessage() (line 187 of modules/contrib/devel/devel_generate/src/DevelGenerateBase.php).

Proposed resolution

Replace line 187 in DevelGenerateBase.php $this->messenger()->addMessage($msg, $type);