11 files declare their use of NotNull in Zircon Profile 8

Abstract2Dot5ApiTest.php in vendor/symfony/validator/Tests/Validator/Abstract2Dot5ApiTest.php

AbstractConstraintValidatorTest.php in vendor/symfony/validator/Tests/Constraints/AbstractConstraintValidatorTest.php

AllValidatorTest.php in vendor/symfony/validator/Tests/Constraints/AllValidatorTest.php

AnnotationLoaderTest.php in vendor/symfony/validator/Tests/Mapping/Loader/AnnotationLoaderTest.php

CollectionValidatorTest.php in vendor/symfony/validator/Tests/Constraints/CollectionValidatorTest.php

CompositeTest.php in vendor/symfony/validator/Tests/Constraints/CompositeTest.php

EntityParent.php in vendor/symfony/validator/Tests/Fixtures/EntityParent.php

NotNullConstraint.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/NotNullConstraint.php

Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\NotNullConstraint.

NotNullValidatorTest.php in vendor/symfony/validator/Tests/Constraints/NotNullValidatorTest.php

XmlFileLoaderTest.php in vendor/symfony/validator/Tests/Mapping/Loader/XmlFileLoaderTest.php

YamlFileLoaderTest.php in vendor/symfony/validator/Tests/Mapping/Loader/YamlFileLoaderTest.php