On Linux, when bundling any package, the FileNotFoundException is logged and .execute method returns null (which causes NPE on our side, which is seen in log)
Log:

==== Running test: com.oracle.appbundlers.tests.functionality.AppInfoParametersTestUnicode::runTest$linux.app-java-api ====
bundling with params: {applicationCategory=SomeCategory, appVersion=1.0.42, classpath=testFxAppWithUtil.jar:Util.jar, vendor=Оракл девелопмент, name=хелловорлд, description=Full application description!, appResources=RelativeFileSet{basedir:/tmp/testBundlerWorkDir9127464227424615693/jars, files:[testFxAppWithUtil.jar, Util.jar]}, mainJar=RelativeFileSet{basedir:/tmp/testBundlerWorkDir9127464227424615693/jars, files:[testFxAppWithUtil.jar]}, title=ХеллоВорлд аппликейшн, email=example@oracle.com}
Creating app bundle: /tmp/testBundlerWorkDir9127464227424615693/bundles
Exception: java.io.FileNotFoundException: /tmp/testBundlerWorkDir9127464227424615693/bundles (Is a directory)
==== Finished test: com.oracle.appbundlers.tests.functionality.AppInfoParametersTestUnicode::runTest$linux.app-java-api ====
java.lang.NullPointerException
at com.oracle.appbundlers.utils.BundlingManager.execute(BundlingManager.java:41)
at com.oracle.appbundlers.tests.functionality.TestBase.runTest(TestBase.java:217)

===============================================
Custom suite
Total tests run: 1, Failures: 1, Skips: 0
===============================================

The bundling is done with Log.setLogger(new Log.Logger(true));