Unexpected exception (Error 990)

Do you know the reason of this exception?

[ObjectDB 2.8.7_03] Unexpected exception (Error 990)
  Generated by OpenJDK 64-Bit Server VM 11.0.8 (on Linux 5.15.0-46-generic).
com.objectdb.o.InternalException: null
com.objectdb.o.InternalException
    at com.objectdb.o.BYR.n(BYR.java:114)
    at com.objectdb.o.BYR.O(BYR.java:207)
    at com.objectdb.o.VUT.j(VUT.java:380)
    at com.objectdb.o.OBI.d(OBI.java:291)
    at com.objectdb.o.OBI.Zg(OBI.java:245)
    at com.objectdb.o.BQI.ZK(BQI.java:153)
    at com.objectdb.o.PRG.d(PRG.java:795)
    at com.objectdb.o.PRG.h(PRG.java:724)
    at com.objectdb.o.PRG.g(PRG.java:560)
    at com.objectdb.o.QRM.Z1(QRM.java:287)
    at com.objectdb.o.MST.Z1(MST.java:1026)
    at com.objectdb.o.WRA.Z1(WRA.java:313)
    at com.objectdb.o.WSM.Z1(WSM.java:117)
    at com.objectdb.o.QRR.k(QRR.java:260)
    at com.objectdb.o.QRR.i(QRR.java:154)
    at com.objectdb.jpa.JpaQuery.getResultList(JpaQuery.java:726)

The stack trace indicates an unexpected error while reading data from the database during a query execution.

It is recommended to use the ObjectDB Doctor to check the integrity of this specific database file. You can find a list of possible reasons for database corruption on the link above. You can also use the Doctor to try the fix the database.

If you get this error with several independent database files then other causes should be investigated. Is this error repeatable? Did it start following a schema change or any other major change? If you can post an example (a database + a simple program or a query that can demonstrates the issue in the Explorer) we can investigate it further.