Error with group summary auto-refresh after adding a project group

To reproduce, add a project group.
It displays the list of Project Groups, and the url is http://example.com/continuum/addProjectGroup.action

Wait for it to automatically refresh. It should re-display the list of project groups, but instead you get a NullPointerException.

java.lang.NullPointerException
at org.apache.maven.continuum.DefaultContinuum.addProjectGroup(DefaultContinuum.java:313)
at org.apache.maven.continuum.web.action.AddProjectGroupAction.execute(AddProjectGroupAction.java:115)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)

This is very similar to http://jira.codehaus.org/browse/CONTINUUM-1560

Workaround: click "Show Project Groups" in the left menu.