java.lang.NullPointerException
        at org.netbeans.modules.python.project.SourceRoots$6.run(SourceRoots.java:307)
        at org.netbeans.modules.python.project.SourceRoots$6.run(SourceRoots.java:287)
        at org.openide.util.Mutex.writeAccess(Mutex.java:433)
        at org.netbeans.modules.python.project.SourceRoots.putRoots(SourceRoots.java:286)
        at org.netbeans.modules.python.project.ui.customizer.PythonProjectProperties.save(PythonProjectProperties.java:194)
        at org.netbeans.modules.python.project.ui.customizer.PythonCustomizerProvider$StoreListener.actionPerformed(PythonCustomizerProvider.java:79)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1.run(CustomizerDialog.java:277)
        at org.openide.util.Mutex.writeAccess(Mutex.java:394)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2.run(CustomizerDialog.java:273)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:577)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1030)