Fix NPE on null description for Document with Collection facet

Caused by: java.lang.NullPointerException
	at org.nuxeo.ecm.collections.jsf.actions.CollectionActionsBean.getSelectedCollectionDescription(CollectionActionsBean.java:295)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.jboss.el.util.ReflectionUtil.invokeMethod(ReflectionUtil.java:335)
	at org.jboss.el.util.ReflectionUtil.invokeMethod(ReflectionUtil.java:280)
	at org.jboss.el.parser.AstMethodSuffix.getValue(AstMethodSuffix.java:59)
	at org.jboss.el.parser.AstValue.getValue(AstValue.java:67)
	at org.jboss.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
	at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
	at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
	at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
	at javax.faces.component.UIOutput.getValue(UIOutput.java:174)
	at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
	at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
	at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
	at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1864)
	at org.richfaces.renderkit.RendererBase.renderChildren(RendererBase.java:277)
	at org.richfaces.renderkit.html.AjaxOutputPanelRenderer.doEncodeChildren(AjaxOutputPanelRenderer.java:57)
	at org.richfaces.renderkit.RendererBase.encodeChildren(RendererBase.java:158)
	at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1857)
	at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:599)
	at org.richfaces.context.MetaComponentEncodingVisitCallback.visit(MetaComponentEncodingVisitCallback.java:83)
	at org.richfaces.context.BaseExtendedVisitContext.invokeVisitCallback(BaseExtendedVisitContext.java:103)
	at org.richfaces.context.ExtendedRenderVisitContext.invokeVisitCallback(ExtendedRenderVisitContext.java:65)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1690)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at javax.faces.component.UIForm.visitTree(UIForm.java:371)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at javax.faces.component.UINamingContainer.visitTree(UINamingContainer.java:174)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at org.nuxeo.ecm.platform.ui.web.binding.alias.UIAliasHolder.visitTree(UIAliasHolder.java:249)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at org.nuxeo.ecm.platform.ui.web.component.holder.UIValueHolder.visitTree(UIValueHolder.java:390)
	at javax.faces.component.UIComponent.visitTree(UIComponent.java:1701)
	at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:406)
	at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:325)
	at org.richfaces.context.ExtendedPartialViewContext.processPartial(ExtendedPartialViewContext.java:255)
	at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1004)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1857)
	at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:435)
	at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
	at org.jboss.seam.jsf.SeamViewHandler.renderView(SeamViewHandler.java:188)
	at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337)
	at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
	at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
	at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
	at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
	... 72 more

select2Actions : org.nuxeo.ecm.platform.ui.select2.Select2ActionsBean@32bfcae5
availablePublicationTrees : [org.nuxeo.ecm.platform.publisher.web.PublishActionsBean$PublicationTreeInformation@162a1f99]
org.nuxeo.theme.negotiation.result.theme : galaxy/default
org.nuxeo.theme.negotiation.result.perspective : default
org.jboss.seam.transaction.synchronizations : org.jboss.seam.transaction.SeSynchronizations@4da19a6a
tabsActionsList : [TAB_VIEW, TAB_EDIT, TAB_FILES_EDIT, TAB_PUBLISH, TAB_RELATIONS, view_comments, TAB_CONTENT_HISTORY, TAB_MANAGE]
org.nuxeo.theme.negotiation.result.engine : default
org.jboss.seam.core.conversationPropagation : org.jboss.seam.core.ConversationPropagation@2ca0ccf7
mobileApplicationActions : org.nuxeo.ecm.mobile.seam.MobileApplicationActionsBean@70f08304
documentRelationManager : org.nuxeo.ecm.platform.relations.services.DocumentRelationService@3e29b589
backendPath : [org.nuxeo.ecm.platform.ui.web.pathelements.DocumentPathElement@478a7f96, org.nuxeo.ecm.platform.ui.web.pathelements.DocumentPathElement@55be758b, org.nuxeo.ecm.platform.ui.web.pathelements.DocumentPathElement@4b1724a7, org.nuxeo.ecm.platform.ui.web.pathelements.DocumentPathElement@5c677674]
actionManager : org.nuxeo.ecm.platform.actions.ActionService@c91e911
org.nuxeo.theme.default.perspective : default
currentServerLocation : org.nuxeo.ecm.platform.util.RepositoryLocation@5c13d641
user_message : An unexpected error occurred. Click on the following links to get more information or go back to the application.
isUserWorkspace : false
restHelper : org.nuxeo.ecm.platform.ui.web.rest.RestHelper@244d5541
notificationManager : org.nuxeo.ecm.platform.ec.notification.service.NotificationService@4a0789de
NuxeoExceptionHandlerMarker : true
org.jboss.seam.transaction.transaction : org.jboss.seam.transaction.Transaction@51183105
currentDocumentIncomingRelations : []
documentThreadedComments : []