NPE in framework-cytoscape.log

My framework-cytoscape.log file is full of this exception...

```
java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor31.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.cytoscape.event.internal.CyListenerAdapter.fireEvent(CyListenerAdapter.java:120)
at org.cytoscape.event.internal.CyEventHelperImpl.fireEvent(CyEventHelperImpl.java:84)
at org.cytoscape.model.internal.TableEventHelperFacade.fireEvent(TableEventHelperFacade.java:69)
at org.cytoscape.model.internal.CyTableImpl.addVirtualColumn(CyTableImpl.java:1013)
at org.cytoscape.io.internal.read.session.Cy3SessionReaderImpl.restoreVirtualColumns(Cy3SessionReaderImpl.java:488)
at org.cytoscape.io.internal.read.session.Cy3SessionReaderImpl.complete(Cy3SessionReaderImpl.java:212)
at org.cytoscape.io.internal.read.session.AbstractSessionReader.run(AbstractSessionReader.java:116)
at org.cytoscape.task.internal.session.OpenSessionTask$OpenSessionWithoutWarningTask.run(OpenSessionTask.java:147)
at org.cytoscape.work.internal.sync.DelegateTask.run(DelegateTask.java:72)
at org.cytoscape.work.internal.task.JDialogTaskManager$TaskRunnable.innerRun(JDialogTaskManager.java:326)
at org.cytoscape.work.internal.task.JDialogTaskManager$TaskRunnable.run(JDialogTaskManager.java:355)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at org.cytoscape.diffusion.internal.ui.OutputPanel.handleEvent(OutputPanel.java:262)
... 19 more
```