TempFileHelper java.lang.IllegalArgumentException: Invalid prefix or suffix

[Michael Hall]

java -Djava.security.policy=HalfPipe/halfpipe_jpkg/outputdir/HalfPipe.app/Contents/app/all.policy SecTemp
WARNING: A terminally deprecated method in java.lang.System has been called
WARNING: System::setSecurityManager has been called by SecTemp (file:/Users/mjh/)
WARNING: Please consider reporting this to the maintainers of SecTemp
WARNING: System::setSecurityManager will be removed in a future release

No exception. So not a valid test case I guess. Different class loaders?