Steps to reproduce :

• Start an already configured Ametys application with an empty repository (unexisting directory)
• Try to launch a total indexation through administration
• You should get the following error :

  2017-04-27 16:38:44,614 ERROR [org.ametys.cms.content.indexing.solr.SolrIndexer] (AmetysRuntimeScheduler_Worker-2;) Error indexing the workspace 'archives'.
  java.lang.NullPointerException
  	at org.ametys.cms.content.indexing.solr.SolrIndexer.unindexAllDocuments(SolrIndexer.java:1623)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.doIndex(SolrWorkspaceIndexer.java:132)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.index(SolrWorkspaceIndexer.java:111)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.indexAllWorkspaces(SolrWorkspaceIndexer.java:89)
  	at org.ametys.cms.indexing.GlobalWorkspaceIndexerSchedulable.execute(GlobalWorkspaceIndexerSchedulable.java:43)
  	at org.ametys.core.schedule.AmetysJob.execute(AmetysJob.java:130)
  	at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
  	at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
  2017-04-27 16:38:44,615 ERROR [org.ametys.core.schedule.AmetysJob$org.ametys.cms.indexing.GlobalWorkspaceIndexerSchedulable] (AmetysRuntimeScheduler_Worker-2;) An error occured during the execution of the Schedulable 'org.ametys.cms.indexing.GlobalWorkspaceIndexerSchedulable'
  org.ametys.cms.indexing.IndexingException: Error indexing the workspace 'archives'.
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.doIndex(SolrWorkspaceIndexer.java:151)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.index(SolrWorkspaceIndexer.java:111)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.indexAllWorkspaces(SolrWorkspaceIndexer.java:89)
  	at org.ametys.cms.indexing.GlobalWorkspaceIndexerSchedulable.execute(GlobalWorkspaceIndexerSchedulable.java:43)
  	at org.ametys.core.schedule.AmetysJob.execute(AmetysJob.java:130)
  	at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
  	at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
  Caused by: java.lang.NullPointerException
  	at org.ametys.cms.content.indexing.solr.SolrIndexer.unindexAllDocuments(SolrIndexer.java:1623)
  	at org.ametys.cms.indexing.solr.SolrWorkspaceIndexer.doIndex(SolrWorkspaceIndexer.java:132)
  	... 6 more