Failure attempting to view a Workflow Model in Admin Center

Steps to reproduce on nightly nuxeo-6.0-SNAPSHOT-20141104-174348

1. Navigate to ADMIN -> Workflow
2. Select one of the two Workflow Models available

Note that an error is reproduced. The relevant Error Context Dump extract is included below:

Request Attributes:

javax.servlet.forward.request_uri : /nuxeo/nxpath/default/document-route-models-root/ParallelDocumentReview@view_documents
javax.servlet.forward.context_path : /nuxeo
javax.servlet.forward.servlet_path : /nxpath/default/document-route-models-root/ParallelDocumentReview@view_documents
javax.servlet.forward.query_string : tabIds=%3A&conversationId=0NXMAIN7
org.nuxeo.theme.url : nxtheme://theme/default/*/jsf-facelets/galaxy/default/default/default
org.nuxeo.theme.default.theme : galaxy/default
org.nuxeo.theme.negotiation.result.collection : default
messageBundle : java.util.PropertyResourceBundle@3dd07531
org.jboss.seam.core.manager : Manager([0NXMAIN7])
currentSuperSpace : DocumentModelImpl(d89f6489-a8a9-4d1d-857b-911ca021d36c, path=/, title=d89f6489-a8a9-4d1d-857b-911ca021d36c)
repositoryManager : org.nuxeo.ecm.core.api.repository.RepositoryManagerImpl@40be03ab
dndConfigHelper : org.nuxeo.ecm.webapp.dnd.DndConfigurationHelper@77f6569f
requestedUrl : nxpath/default/document-route-models-root/ParallelDocumentReview@view_documents?tabIds=%3A&old_conversationId=0NXMAIN7
securityError : false
org.jboss.seam.web.requestContextPath : /nuxeo
adminMessageActivated : false
nuxeo.disable.redirect.wrapper : true
nxDevModeSet : true
currentDomain : DocumentModelImpl(6bc3c3d6-de9c-4d54-8b95-3b73007cba18, path=/default-domain, title=6bc3c3d6-de9c-4d54-8b95-3b73007cba18)
seamReload : org.nuxeo.ecm.webapp.seam.NuxeoSeamHotReloader@4db11e40
nuxeoAliasBean : org.nuxeo.ecm.platform.ui.web.binding.alias.NuxeoAliasBean@27392399
currentDocument : DocumentModelImpl(1826737c-18d0-46a1-80ea-5e5948431bce, path=/document-route-models-root/ParallelDocumentReview, title=wf.parallelDocumentReview.ParallelDocumentReview)
lockActions : ERROR TRYING TO GET THIS REQUEST ATTRIBUTE VALUE
com.sun.faces.context.ExternalContextFactoryImpl_KEY : com.sun.faces.context.ExternalContextImpl@185025ed
currentWorkspace : DocumentModelImpl(abbb3f2b-75e4-4027-9a8c-bf09f1286d78, path=/default-domain/workspaces/test.1415120834793, title=abbb3f2b-75e4-4027-9a8c-bf09f1286d78)
exception_message : /select_route_elements_type.xhtml @22,80 <rich:modalPanel> Tag Library supports namespace: http://richfaces.org/rich, but no tag was defined for name: modalPanel
org.jboss.seam.web.servletContexts : org.jboss.seam.web.ServletContexts@35e9f713
org.jboss.seam.core.events : org.jboss.seam.core.Events@135c1c0c
org.jboss.seam.web.requestServletPath : /view_documents.faces
nuxeoDriveIsUnderSynchronizationRoot : false
DocumentView : DocumentViewImpl [documentLocation=DocumentLocationImpl [docIdRef=null, docPathRef=/document-route-models-root/ParallelDocumentReview, docRef=/document-route-models-root/ParallelDocumentReview, serverName=default], parameters=

{tabIds=:, conversationId=0NXMAIN7, tabId=null, subTabId=null, language=null, mainTabId=null}

, patternName=default, subURI=null, tabId=null, viewId=view_documents]
deleteActions : org.nuxeo.ecm.webapp.action.DeleteActionsBean@43561c2
isInsidePersonalWorkspace : false
org.nuxeo.theme.default.engine : default
org.nuxeo.theme.negotiation.result.mode : *
select2Converter : org.nuxeo.ecm.platform.ui.select2.Select2Converter@4ca509b6
stackTrace : javax.servlet.ServletException: /select_route_elements_type.xhtml @22,80 <rich:modalPanel> Tag Library supports namespace: http://richfaces.org/rich, but no tag was defined for name: modalPanel
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:659)