Creating a comment breaks the seach and the dashboard

When comments have been created the search is partially broken and the dashboard generate an HTTP 500 error.
This may be due to the fact that comment are documents that does not have the common schema (the one that is used by seach).

A quick fix would be to add the common schema.

Partial traceback :
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:283)
at org.jboss.seam.ui.facelet.MethodExpressionHelper.invokeTheExpression(MethodExpressionHelper.java:102)
at org.jboss.seam.ui.facelet.ParamMethodExpression.invoke(ParamMethodExpression.java:62)
at com.sun.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:68)
... 66 more
Caused by: org.nuxeo.ecm.core.query.QueryException: getDocumentModels failed
at org.nuxeo.ecm.core.jcr.JCRQueryResult.getDocumentModels(JCRQueryResult.java:297)
at org.nuxeo.ecm.core.api.AbstractSession.query(AbstractSession.java:774)
... 228 more
Caused by: java.lang.NullPointerException
at org.nuxeo.ecm.core.api.DocumentModelFactory.exportSchema(DocumentModelFactory.java:181)
at org.nuxeo.ecm.core.api.DocumentModelFactory.createDocumentModel(DocumentModelFactory.java:115)
at org.nuxeo.ecm.core.jcr.JCRQueryResult.getDocumentModels(JCRQueryResult.java:291)
... 229 more