Newbie question about environment initialization

Hi,
I'm trying to set up environment to develop DI solution with java, but my code fails when call KettleEnvironment.init() method.
I'm working with windows 7 OS and I have configured environment variable like that: KETTLE_HOME = C:\Users\X (where in X there is .kettle dir). What's wrong?
Thanks in advance.
Here is the stack trace:

Exception in thread "main" java.lang.ExceptionInInitializerError
at org.pentaho.di.core.KettleClientEnvironment.createKettleHome(KettleClientEnvironment.java:116)
at org.pentaho.di.core.KettleClientEnvironment.init(KettleClientEnvironment.java:72)
at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:91)
at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:69)
at it.fabricalab.edu.di.kettle.main.Main.main(Main.java:39)
Caused by: java.lang.NullPointerException
at org.pentaho.di.laf.BasePropertyHandler.getProperty(BasePropertyHandler.java:86)
at org.pentaho.di.core.Const.getUserBaseDir(Const.java:1716)
at org.pentaho.di.core.Const.getKettleDirectory(Const.java:1706)
at org.pentaho.di.core.Const.<clinit>(Const.java:201)
... 5 more