When I'm trying to use srcfiles argument without srcdir argument I get this result:
dmitry.ginzburg@oracle-ginzburg:/local/work/packagerTestsSuite/apps/HelloWorld$ javafxpackager -signJar -v -srcfiles dist/HelloWorld.jar -keyStore pkg-tests-keystore -outdir dist -alias pkgtests -storePass pkgtests -keyPass pkgtests
Exception in thread "main" java.lang.NullPointerException
at com.sun.javafx.tools.resource.PackagerResource.createFile(PackagerResource.java:133)
at com.sun.javafx.tools.resource.PackagerResource.<init>(PackagerResource.java:28)
at com.sun.javafx.tools.packager.SignJarParams.addResource(SignJarParams.java:50)
at com.sun.javafx.tools.packager.Main.addResources(Main.java:84)
at com.sun.javafx.tools.packager.Main.main(Main.java:358)

Without verbose argument:
dmitry.ginzburg@oracle-ginzburg:/local/work/packagerTestsSuite/apps/HelloWorld$ javafxpackager -signJar -srcfiles dist/HelloWorld.jar -keyStore pkg-tests-keystore -outdir dist -alias pkgtests -storePass pkgtests -keyPass pkgtests
null

I attach this HelloWorld project: to see this result you should firstly call ant -f simple-build.xml jar, then use one of the commands above.