8 files declare their use of EntityContentBase

Book.php in core/modules/book/src/Plugin/migrate/destination/Book.php
DestinationCategoryTest.php in core/modules/migrate_drupal/tests/src/Kernel/Plugin/migrate/DestinationCategoryTest.php
EntityComment.php in core/modules/comment/src/Plugin/migrate/destination/EntityComment.php
EntityContentBaseTest.php in core/modules/migrate/tests/src/Unit/Plugin/migrate/destination/EntityContentBaseTest.php
EntityFile.php in core/modules/file/src/Plugin/migrate/destination/EntityFile.php
EntityUser.php in core/modules/user/src/Plugin/migrate/destination/EntityUser.php
IdConflictForm.php in core/modules/migrate_drupal_ui/src/Form/IdConflictForm.php
MigrateEntityContentBaseTest.php in core/modules/migrate/tests/src/Kernel/MigrateEntityContentBaseTest.php

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