java.lang.NullPointerException at sun.awt.X11.XSelection.checkChange(XSelection.java:749) at sun.awt.X11.XSelection.access$200(XSelection.java:30) at sun.awt.X11.XSelection$SelectionEventHandler.dispatchEvent(XSelection.java:758) at sun.awt.X11.XToolkit.dispatchEvent(XToolkit.java:482) at sun.awt.X11.XToolkit.run(XToolkit.java:626) at sun.awt.X11.XToolkit.run(XToolkit.java:560) at java.lang.Thread.run(Thread.java:619)