dbseer_front_end errors

[XiaodiLiu]

the environment
java 1.8
octave 4.0.1
i tried to install dbseer_front_end step by step according to insall.md, but some errors occured .
i am not able to find the reason and really need your help.....
i executed the following commands:

1. i changed relative numbers from 6 to 8 in dbseer_front_end.xml
   for example:
   <property name="compiler.args.dbseer_front_end" value="-encoding UTF-8 -source 1.6 ${compiler.args} "/>
   to
   <property name="compiler.args.dbseer_front_end" value="-encoding UTF-8 -source 1.8 ${compiler.args} "/>
2. lauch the dbseer gui
   root$ java -Xmx2048M -jar out/artifacts/dbseer_front_end_jar/dbseer_front_end.jar ./dbseer.ini
   some errors occured:
   `Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
   at dbseer.gui.DBSeerGUI$2.run(DBSeerGUI.java:487)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
   at java.awt.EventQueue.access$500(EventQueue.java:97)
   at java.awt.EventQueue$3.run(EventQueue.java:709)
   at java.awt.EventQueue$3.run(EventQueue.java:703)
   at java.security.AccessController.doPrivileged(Native Method)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

thanks a lot !