java.lang.NullPointerException: The p parameter cannot be null
   at org.openide.util.Parameters.notNull(Parameters.java:89)
   at org.netbeans.api.project.ProjectUtils.getSources(ProjectUtils.java:109)
   at org.netbeans.modules.java.freeform.Classpaths$RemoveSources.<init>(Classpaths.java:773)
   at org.netbeans.modules.java.freeform.Classpaths.createCompileClasspath(Classpaths.java:436)
   at org.netbeans.modules.java.freeform.Classpaths.createProcessorClasspath(Classpaths.java:496)
   at org.netbeans.modules.java.freeform.Classpaths.access$600(Classpaths.java:126)
   at org.netbeans.modules.java.freeform.Classpaths$MutableClassPathImplementation.initRoots(Classpaths.java:607)
   at org.netbeans.modules.java.freeform.Classpaths$MutableClassPathImplementation.change(Classpaths.java:646)
   at org.netbeans.modules.java.freeform.Classpaths.pathsChanged(Classpaths.java:551)
   at org.netbeans.modules.java.freeform.Classpaths.configurationXmlChanged(Classpaths.java:535)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$3.run(AntProjectHelper.java:524)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$3.run(AntProjectHelper.java:519)
   at org.netbeans.modules.openide.util.DefaultMutexImplementation.readAccess(DefaultMutexImplementation.java:252)
   at org.openide.util.Mutex.readAccess(Mutex.java:218)
   at org.netbeans.spi.project.support.ant.AntProjectHelper.fireChange(AntProjectHelper.java:519)
   at org.netbeans.spi.project.support.ant.AntProjectHelper.access$1700(AntProjectHelper.java:114)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$ActionImpl.run(AntProjectHelper.java:1414)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$ActionImpl.run(AntProjectHelper.java:1403)
   at org.netbeans.modules.openide.util.DefaultMutexImplementation.readAccess(DefaultMutexImplementation.java:252)
   at org.openide.util.Mutex.readAccess(Mutex.java:218)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$RunnableImpl.run(AntProjectHelper.java:1399)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443)
   at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68)
   at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058)