CmsJcrTree is virtual can throw NPE during tree refresh

at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at
org.hippoecm.frontend.plugins.cms.browse.tree.CmsJcrTree.isVirtual(CmsJcrTree.java:89)
at
org.hippoecm.frontend.plugins.cms.browse.tree.CmsJcrTree.getCss(CmsJcrTree.java:66)
at
org.hippoecm.frontend.plugins.cms.browse.tree.CmsJcrTree.access$000(CmsJcrTree.java:33)
at
org.hippoecm.frontend.plugins.cms.browse.tree.CmsJcrTree$1.onComponentTag(CmsJcrTree.java:50)
at org.apache.wicket.Component.renderComponent(Component.java:2451)
at
org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1411)
at org.apache.wicket.Component.render(Component.java:2317)
at
org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1297)
at
org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1476)
at
org.apache.wicket.markup.html.link.AbstractLink.onComponentTagBody(AbstractLink.java:165)
at org.apache.wicket.Component.renderComponent(Component.java:2480)