Intermittent failure java.lang.NullPointerException: name can't be null with IBM 1.6 and encryptionECB/encryptDatabase test

Very rarely on IBM 1.6 on Linux we get this failure with the
encryptDatabase test.

The trace looks like:

java.lang.NullPointerException: name can't be null
at java.io.FilePermission.init(FilePermission.java:183)
at
java.io.FilePermission.<init>(FilePermission.java:267)
at
java.lang.SecurityManager.checkRead(SecurityManager.java:871)
at java.io.File.list(File.java:983)
at
org.apache.derby.impl.store.raw.data.BaseDataFileFactory.run(Bas
eDataFileFactory.java:2640)
at
java.security.AccessController.doPrivileged(AccessController.jav
a:251)
at
org.apache.derby.impl.store.raw.data.BaseDataFileFactory.removeS
tubs(BaseDataFileFactory.java:1591)
at
org.apache.derby.impl.store.raw.data.BaseDataFileFactory.stop(Ba
seDataFileFactory.java:499)
at
org.apache.derby.impl.services.monitor.TopService.stop(TopServic
e.java:405)
at
org.apache.derby.impl.services.monitor.TopService.shutdown(TopSe
rvice.java:349)
at
org.apache.derby.impl.services.monitor.BaseMonitor.shutdown(Base
Monitor.java:239)
at
org.apache.derby.impl.db.DatabaseContextImpl.cleanupOnError(Data
baseContextImpl.java:60)
at
org.apache.derby.iapi.services.context.ContextManager.cleanupOnE
rror(ContextManager.java:332)
at
org.apache.derby.impl.jdbc.TransactionResourceImpl.cleanupOnErro
r(TransactionResourceImpl.java:419)
at
org.apache.derby.impl.jdbc.EmbedConnection.<init>(EmbedConnec
tion.java:584)
at
org.apache.derby.jdbc.Driver40.getNewEmbedConnection(Driver40.ja
va:68)
at
org.apache.derby.jdbc.InternalDriver.connect(InternalDriver.java
:238)
at
org.apache.derby.jdbc.AutoloadedDriver.connect(AutoloadedDriver.
java:119)
at
java.sql.DriverManager.getConnection(DriverManager.java:316)
at
java.sql.DriverManager.getConnection(DriverManager.java:297)
at
org.apache.derby.impl.tools.ij.ij.dynamicConnection(ij.java:1329
)
at
org.apache.derby.impl.tools.ij.ij.ConnectStatement(ij.java:1179)

at
org.apache.derby.impl.tools.ij.ij.ijStatement(ij.java:1007)
at
org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(utilMain.j
ava:328)
at
org.apache.derby.impl.tools.ij.utilMain.go(utilMain.java:248)
at org.apache.derby.impl.tools.ij.Main.go(Main.java:215)
at
org.apache.derby.impl.tools.ij.Main.mainCore(Main.java:181)
at org.apache.derby.impl.tools.ij.Main.main(Main.java:73)
at org.apache.derby.tools.ij.main(ij.java:59)

or something similar. It happens at different areas of the code
but always with File.list().

I haven't been able to reproduce despite running the test 1500 times. I also haven't figured out yet how to get the java.lang.NullPointerException: name can't be null message in a stand alone java program.

I will attache the test files.