Can't decode the license file

[epris]

Dear all,
It's my first time with License3j. I 'm following the tutorial "http://verhas.github.io/License3j/tuto.html" but I have a problem in the last step.
If i write
license3j.bat decode --license-file=license.out --keyring-file="C:\Users\Utente\AppData\Roaming\gnupg\pubring.gpg"
the following error is reported
log4j:WARN No appenders could be found for logger (com.verhas.licensor.License).

log4j:WARN Please initialize the log4j system properly.
Usage: java -cp license3j.jar License3j decode options
mandatory options are:
--license-file, --keyring-file, [ --output ] [--charset]
Exception in thread "main" java.lang.NullPointerException
at java.io.ByteArrayInputStream.(ByteArrayInputStream.java:106)
at com.verhas.licensor.License.setLicenseEncoded(License.java:543)
at com.verhas.licensor.License.setLicenseEncoded(License.java:508)
at com.verhas.licensor.License.setLicenseEncodedFromFile(License.java:48
9)
at License3j.decode(License3j.java:102)
at License3j.main(License3j.java:173)
"cmd" non è riconosciuto come comando interno o esterno,
un programma eseguibile o un file batch.

Can you help me?