7 files declare their use of DefaultSingleLazyPluginCollection

ActionPluginCollection.php in core/lib/Drupal/Core/Action/ActionPluginCollection.php
BlockPluginCollection.php in core/modules/block/src/BlockPluginCollection.php
DefaultSingleLazyPluginCollectionTest.php in core/tests/Drupal/Tests/Core/Plugin/DefaultSingleLazyPluginCollectionTest.php
MediaType.php in core/modules/media/src/Entity/MediaType.php
RestResourceConfig.php in core/modules/rest/src/Entity/RestResourceConfig.php
SearchPluginCollection.php in core/modules/search/src/Plugin/SearchPluginCollection.php
Workflow.php in core/modules/workflows/src/Entity/Workflow.php

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