java.lang.NullPointerException: The toOpen parameter cannot be null
   at org.openide.util.Parameters.notNull(Parameters.java:89)
   at org.netbeans.api.java.source.ui.ElementOpen.open(ElementOpen.java:172)
   at org.netbeans.api.java.source.ui.ElementOpen.access$100(ElementOpen.java:73)
   at org.netbeans.api.java.source.ui.ElementOpen$2.run(ElementOpen.java:155)
   at org.netbeans.modules.progress.ui.RunOffEDTImpl$1.run(RunOffEDTImpl.java:169)
   at org.openide.util.RequestProcessor$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)