ADDITIONAL SYSTEM INFORMATION :
Mac OS X 10.15.5
java --version
openjdk 16-ea 2021-03-16
OpenJDK Runtime Environment (build 16-ea+6-203)
OpenJDK 64-Bit Server VM (build 16-ea+6-203, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
release 15 would always create a temporary working directory itself. release 16 throws an exception.

REGRESSION : Last worked in version 15

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run jpackage with a --temp directory specified under jdk 15. It works.
Run jpackage with a --temp directory specified under jdk 16. It fails.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A .dmg should be produced.
ACTUAL -
jpackage --type dmg --app-image /Users/davidjlgradwell/NetBeansDev/PKBAnt/pkg23July2020/PKB-1.0.pkg --name PKBInstaller --dest /Users/davidjlgradwell/NetBeansDev/PKBAnt/pkg23July2020/output --resource-dir /Users/davidjlgradwell/NetBeansDev/PKBAnt/resources --temp /Users/davidjlgradwell/NetBeansDev/PKBAnt/pkg23July2020/temp --verbose
WARNING: Using incubator modules: jdk.incubator.jpackage
[14:31:56.815] java.lang.NullPointerException: Cannot read the array length because the return value of "java.io.File.list()" is null
at jdk.incubator.jpackage/jdk.incubator.jpackage.internal.DeployParams.validate(DeployParams.java:209)
at jdk.incubator.jpackage/jdk.incubator.jpackage.internal.Arguments.processArguments(Arguments.java:510)
at jdk.incubator.jpackage/jdk.incubator.jpackage.main.Main.execute(Main.java:98)
at jdk.incubator.jpackage/jdk.incubator.jpackage.main.Main.main(Main.java:52)

---------- BEGIN SOURCE ----------
Take an app image created previously with jpackage and run a command similar to the above to create a .dmg
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Remove the --temp parameter and it works OK, producing the expected .dmg

FREQUENCY : always