Change record status: 
Project: 
Introduced in branch: 
9.1.x
Introduced in version: 
9.1.0
Description: 

MigrationPluginManager::createInstancesByTag will now return an empty array when there are no migrations with the provided tags. Previously, all migrations were returned.

For example, consider that there are no migrations with the tag 'foo' and the following is executed.

$tags = ['foo'];
$migrations = \Drupal\migrate\Plugin\MigrationPluginManager::createInstancesByTag($tags);

The migrations returned before and after this change are:
Before

$migrations will contain all discovered migrations.

After

$migrations will be an empty array.

Impacts: 
Module developers