java.lang.IllegalArgumentException: Empty command
   at java.lang.Runtime.exec(Runtime.java:444)
   at java.lang.Runtime.exec(Runtime.java:347)
   at org.netbeans.modules.diff.options.DiffOptionsPanel$CheckCommand.run(DiffOptionsPanel.java:342)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1423)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)