java.lang.NullPointerException
	at org.ametys.core.ui.RibbonConfigurationManager._resolveReferences(RibbonConfigurationManager.java:569)
	at org.ametys.core.ui.RibbonConfigurationManager._createGroupForUser(RibbonConfigurationManager.java:518)
	at org.ametys.core.ui.RibbonConfigurationManager._generateTabGroups(RibbonConfigurationManager.java:488)
	at org.ametys.core.ui.RibbonConfigurationManager.saxRibbonDefinition(RibbonConfigurationManager.java:421)
	at org.ametys.plugins.core.ui.WorkspaceGenerator.doGenerate(WorkspaceGenerator.java:153)
	at org.ametys.plugins.core.ui.WorkspaceGenerator.generate(WorkspaceGenerator.java:124)
	at org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.processXMLPipeline(AbstractProcessingPipeline.java:581)
	at org.apache.cocoon.components.pipeline.impl.AbstractCachingProcessingPipeline.processXMLPipeline(AbstractCachingProcessingPipeline.java:301)
	at org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.process(AbstractProcessingPipeline.java:782)
	at org.apache.cocoon.components.source.impl.SitemapSource.toSAX(SitemapSource.java:414)
	at org.apache.cocoon.components.source.SourceUtil.toSAX(SourceUtil.java:101)
	at org.apache.cocoon.components.source.SourceUtil.parse(SourceUtil.java:321)
	at org.apache.cocoon.sitemap.ContentAggregator.generate(ContentAggregator.java:125)