Not working with JDK11

[Ralf-lamasoft]

With JDK11 initialization works, but there seems to be no proper way to close the database. It breaks with an exception:
Exception in thread "AWT-EventQueue-0" java.lang.NoSuchMethodError: sun.nio.ch.DirectBuffer.cleaner()Lsun/misc/Cleaner;
at org.apache.jdbm.StorageDiskMapped.unmapBuffer(StorageDiskMapped.java:125).
JDK9 introduced java.lang.ref.Cleaner as replacement for sun.misc.Cleaner!