Issue #2449: ​​​​​​​Unexpected internal exception

Unexpected internal exception
[ObjectDB 2.8.0_04] Unexpected exception (Error 990)
  Generated by OpenJDK 64-Bit Server VM 1.8.0_212 (on Linux 4.19.14-041914-generic).
Please report this error on http://www.objectdb.com/issue/new
com.objectdb.o.InternalException: java.lang.NullPointerException: null
java.lang.NullPointerException
    at com.objectdb.o.OBM.aO(OBM.java:396)
    at com.objectdb.o.OBM.aO(OBM.java:270)
    at com.objectdb.jpa.EMImpl.persist(EMImpl.java:415)
    at au2019.backend.core.services.AuDatabase.save(persistence.kt:183)
    at exp.koin.test.JUnitTest2$2$1.invoke(JUnitTest2.kt:30)
    at exp.koin.test.JUnitTest2$2$1.invoke(JUnitTest2.kt:14)
    at au2019.backend.core.services.AuDatabase.transact(persistence.kt:153)
    at exp.koin.test.JUnitTest2$2.invokeSuspend(JUnitTest2.kt:29)
    at exp.koin.test.JUnitTest2$2.invoke(JUnitTest2.kt)
    at io.kotlintest.runner.jvm.TestCaseExecutor$executeTest$supervisorJob$1$invokeSuspend$$inlined$map$lambda$1.invokeSuspend(TestCaseExecutor.kt:121)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:233)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

Thank you for this report. The stack trace indicates an issue with the metadata that ObjectDB holds on a specific class. Please check the hierarchy of the relevant class (that its instance is persisted to the database when the exception is thrown). Do you still get the exception after rebuilding your project and enhancing all the classes?