ADDITIONAL SYSTEM INFORMATION :
Mac OSX Catalina 10.15.5 (19F101)
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 :
jpackage --type dmg --app-image repeatably gives:
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)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Set up appropriate file structure and Apple Developer certificates. Prove that jpacage runs well with other options.

Try the combination of --type dmg --app-image as for example the following:

jpackage --type dmg --app-image /Users/davidjlgradwell/NetBeansDev/PKBAnt/jpackagepkgoutput23rdJuly2020stapledKeep/PKB-1.0.pkg --name PKBInstaller --dest /Users/davidjlgradwell/NetBeansDev/PKBAnt/jpackagedmgoutputpkg23july2020 --resource-dir /Users/davidjlgradwell/NetBeansDev/PKBAnt/resources --temp /Users/davidjlgradwell/NetBeansDev/PKBAnt/jpackageappimagepkg23july2020 --verbose


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Would expect a .dmg to be produced.
ACTUAL -
WARNING: Using incubator modules: jdk.incubator.jpackage
[14:26:18.002] 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 ----------
Needs a complete application package. I used one created successfully using jpackage immediately before.
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
No work around

FREQUENCY : always