Tagcloud cannot be edited when document has mixins with child nodes

When the tag cloud document has child nodes that do not have a primary type from the tcmp namespace, the tagcloud cannot be edited.

The console logs an error:

04.01.2011 19:19:46 ERROR [org.onehippo.forge.tcmp.common.Utils.getModelForNode():103]
java.lang.NullPointerException
at org.onehippo.forge.tcmp.common.Utils.getModelForNode(Utils.java:100)
at org.onehippo.forge.tcmp.model.TagCloud.getModelMap(TagCloud.java:88)
at org.onehippo.forge.tcmp.preview.PreviewPlugin$TagCloudView.getItemModels(PreviewPlugin.java:245)
at org.apache.wicket.markup.repeater.RefreshingView.onPopulate(RefreshingView.java:94)
at org.apache.wicket.markup.repeater.AbstractRepeater.onBeforeRender(AbstractRepeater.java:131)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1071)
at org.apache.wicket.Component.beforeRender(Component.java:1105)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1753)

Ignoring child nodes of unknown node type seems reasonable.