Projection interface with Optional property not working on Java 16

Hi all,

I'm trying to migrate a spring-boot 2.5.1 project to Java 16 and I encountered the following ExceptionCaused by: java.lang.reflect.InaccessibleObjectException: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76

As the spring-boot documentation claims compatibility to Java 16, it made me curious and I tried to track the issue down with a minimal reproducer project from https://start.spring.io.

It turns out, that the problem occurs only, if there is a query Method returning a projection interface and the projection interface contains an Optional property like this (full reproducer project here: https://github.com/skuzzle/mongo-repository-jdk16-problem):

public interface TestDocumentRepository extends MongoRepository<TestDocument, String> {
    List<TestDocumentProjection> findByName(String name);
}

public interface TestDocumentProjection {
    Optional<String> getNullableProperty();
}

Full stack trace:

java.lang.IllegalStateException: Failed to load ApplicationContext
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:132) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:124) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:118) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:83) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.boot.test.autoconfigure.SpringBootDependencyInjectionTestExecutionListener.prepareTestInstance(SpringBootDependencyInjectionTestExecutionListener.java:43) ~[spring-boot-test-autoconfigure-2.5.1.jar:2.5.1]
	at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:244) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.test.context.junit.jupiter.SpringExtension.postProcessTestInstance(SpringExtension.java:138) ~[spring-test-5.3.8.jar:5.3.8]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$6(ClassBasedTestDescriptor.java:350) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.executeAndMaskThrowable(ClassBasedTestDescriptor.java:355) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$7(ClassBasedTestDescriptor.java:350) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~[na:na]
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
	at java.base/java.util.stream.StreamSpliterators$WrappingSpliterator.forEachRemaining(StreamSpliterators.java:312) ~[na:na]
	at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:735) ~[na:na]
	at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:734) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[na:na]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeTestInstancePostProcessors(ClassBasedTestDescriptor.java:349) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$instantiateAndPostProcessTestInstance$4(ClassBasedTestDescriptor.java:270) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.instantiateAndPostProcessTestInstance(ClassBasedTestDescriptor.java:269) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$2(ClassBasedTestDescriptor.java:259) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at java.base/java.util.Optional.orElseGet(Optional.java:364) ~[na:na]
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$3(ClassBasedTestDescriptor.java:258) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.execution.TestInstancesProvider.getTestInstances(TestInstancesProvider.java:31) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$prepare$0(TestMethodTestDescriptor.java:101) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:100) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:65) ~[junit-jupiter-engine-5.7.2.jar:5.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$prepare$1(NodeTestTask.java:111) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.prepare(NodeTestTask.java:111) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:79) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) ~[junit-platform-engine-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:84) ~[junit-platform-launcher-1.7.2.jar:1.7.2]
	at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:98) ~[.cp/:na]
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:40) ~[.cp/:na]
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:529) ~[.cp/:na]
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:756) ~[.cp/:na]
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:452) ~[.cp/:na]
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210) ~[.cp/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testDocumentRepository' defined in com.example.demo.TestDocumentRepository defined in @EnableMongoRepositories declared on MongoRepositoriesRegistrar.EnableMongoRepositoriesConfiguration: Invocation of init method failed; nested exception is org.springframework.data.repository.query.QueryCreationException: Could not create query for public abstract java.util.List com.example.demo.TestDocumentRepository.findByName(java.lang.String)! Reason: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76; nested exception is java.lang.reflect.InaccessibleObjectException: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1786) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:602) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:925) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.8.jar:5.3.8]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.8.jar:5.3.8]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-2.5.1.jar:2.5.1]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:434) ~[spring-boot-2.5.1.jar:2.5.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:338) ~[spring-boot-2.5.1.jar:2.5.1]
	at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:123) ~[spring-boot-test-2.5.1.jar:2.5.1]
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:99) ~[spring-test-5.3.8.jar:5.3.8]
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124) ~[spring-test-5.3.8.jar:5.3.8]
	... 70 common frames omitted
Caused by: org.springframework.data.repository.query.QueryCreationException: Could not create query for public abstract java.util.List com.example.demo.TestDocumentRepository.findByName(java.lang.String)! Reason: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76; nested exception is java.lang.reflect.InaccessibleObjectException: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76
	at org.springframework.data.repository.query.QueryCreationException.create(QueryCreationException.java:101) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.lookupQuery(QueryExecutorMethodInterceptor.java:106) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.lambda$mapMethodsToQuery$1(QueryExecutorMethodInterceptor.java:94) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133) ~[na:na]
	at java.base/java.util.Collections$UnmodifiableCollection$1.forEachRemaining(Collections.java:1056) ~[na:na]
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682) ~[na:na]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.mapMethodsToQuery(QueryExecutorMethodInterceptor.java:96) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.lambda$new$0(QueryExecutorMethodInterceptor.java:86) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at java.base/java.util.Optional.map(Optional.java:260) ~[na:na]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.<init>(QueryExecutorMethodInterceptor.java:86) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.RepositoryFactorySupport.getRepository(RepositoryFactorySupport.java:360) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.lambda$afterPropertiesSet$5(RepositoryFactoryBeanSupport.java:323) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.util.Lazy.getNullable(Lazy.java:230) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.util.Lazy.get(Lazy.java:114) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.afterPropertiesSet(RepositoryFactoryBeanSupport.java:329) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mongodb.repository.support.MongoRepositoryFactoryBean.afterPropertiesSet(MongoRepositoryFactoryBean.java:119) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1845) ~[spring-beans-5.3.8.jar:5.3.8]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1782) ~[spring-beans-5.3.8.jar:5.3.8]
	... 85 common frames omitted
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make private java.util.Optional(java.lang.Object) accessible: module java.base does not "opens java.util" to unnamed module @26f67b76
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357) ~[na:na]
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297) ~[na:na]
	at java.base/java.lang.reflect.Constructor.checkCanSetAccessible(Constructor.java:188) ~[na:na]
	at java.base/java.lang.reflect.Constructor.setAccessible(Constructor.java:181) ~[na:na]
	at org.springframework.util.ReflectionUtils.makeAccessible(ReflectionUtils.java:202) ~[spring-core-5.3.8.jar:5.3.8]
	at org.springframework.data.mapping.PreferredConstructor.<init>(PreferredConstructor.java:64) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.model.PreferredConstructorDiscoverer$Discoverers.buildPreferredConstructor(PreferredConstructorDiscoverer.java:222) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.model.PreferredConstructorDiscoverer$Discoverers.access$200(PreferredConstructorDiscoverer.java:91) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.model.PreferredConstructorDiscoverer$Discoverers$1.discover(PreferredConstructorDiscoverer.java:134) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.model.PreferredConstructorDiscoverer.discover(PreferredConstructorDiscoverer.java:79) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.model.BasicPersistentEntity.<init>(BasicPersistentEntity.java:112) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mongodb.core.mapping.BasicMongoPersistentEntity.<init>(BasicMongoPersistentEntity.java:77) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mongodb.core.mapping.MongoMappingContext.createPersistentEntity(MongoMappingContext.java:91) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mongodb.core.mapping.MongoMappingContext.createPersistentEntity(MongoMappingContext.java:40) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mapping.context.AbstractMappingContext.addPersistentEntity(AbstractMappingContext.java:367) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at java.base/java.util.Collections$SingletonSet.forEach(Collections.java:4872) ~[na:na]
	at org.springframework.data.mapping.context.AbstractMappingContext$PersistentPropertyCreator.createAndRegisterProperty(AbstractMappingContext.java:563) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~[na:na]
	at java.base/java.util.HashMap$ValueSpliterator.forEachRemaining(HashMap.java:1766) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) ~[na:na]
	at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150) ~[na:na]
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596) ~[na:na]
	at org.springframework.data.mapping.context.AbstractMappingContext$PersistentPropertyCreator.addPropertiesForRemainingDescriptors(AbstractMappingContext.java:538) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.context.AbstractMappingContext.addPersistentEntity(AbstractMappingContext.java:385) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:258) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:201) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentEntity(AbstractMappingContext.java:87) ~[spring-data-commons-2.5.1.jar:2.5.1]
	at org.springframework.data.mongodb.repository.query.MongoQueryMethod.getEntityInformation(MongoQueryMethod.java:157) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mongodb.repository.query.AbstractMongoQuery.<init>(AbstractMongoQuery.java:78) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mongodb.repository.query.PartTreeMongoQuery.<init>(PartTreeMongoQuery.java:64) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.mongodb.repository.support.MongoRepositoryFactory$MongoQueryLookupStrategy.resolveQuery(MongoRepositoryFactory.java:207) ~[spring-data-mongodb-3.2.1.jar:3.2.1]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.lookupQuery(QueryExecutorMethodInterceptor.java:102) ~[spring-data-commons-2.5.1.jar:2.5.1]
	... 107 common frames omitted

Java version:

./mvnw -version
Apache Maven 3.8.1 (05c21c65bdfed0f71a2f2ada8b84da59348c4c5d)
Maven home: C:\Users\Simon\.m2\wrapper\dists\apache-maven-3.8.1-bin\2l5mhf2pq2clrde7f7qp1rdt5m\apache-maven-3.8.1
Java version: 16.0.1, vendor: Oracle Corporation, runtime: C:\Program Files\Java\jdk-16.0.1
Default locale: de_DE, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"

The reproducer centers on TestDocumentRepository.findByName and TestDocumentProjection.getNullableProperty in the linked minimal project. Start by running it on Java 16 and tracing repository query creation around the Optional projection. Done means the projection loads without InaccessibleObjectException and the reproducer succeeds.