13 files declare their use of UserMergeException in User Merge 2.x

ActionBlock.php in src/Plugin/UserMerge/Action/ActionBlock.php

ActionBlockTest.php in tests/src/Kernel/ActionBlockTest.php

ActionDelete.php in src/Plugin/UserMerge/Action/ActionDelete.php

ActionDeleteTest.php in tests/src/Kernel/ActionDeleteTest.php

BatchGenerator.php in src/BatchGenerator.php

MultiStepFormController.php in src/Controller/MultiStepFormController.php

PropertyComment.php in src/Plugin/UserMerge/Property/PropertyComment.php

PropertyEntityReference.php in src/Plugin/UserMerge/Property/PropertyEntityReference.php

PropertyFlag.php in src/Plugin/UserMerge/Property/PropertyFlag.php

PropertyMessage.php in src/Plugin/UserMerge/Property/PropertyMessage.php

PropertyNode.php in src/Plugin/UserMerge/Property/PropertyNode.php

ReviewFormSwitcher.php in src/ReviewFormSwitcher.php

ReviewFormSwitcherTest.php in tests/src/Unit/ReviewFormSwitcherTest.php