Error in the logs after upgrade from 7.0 to 7.3M2

2015-11-04 13:11:51.954:INFO:oxtjl.NotifyListener:main: ----------------------------------
2015-11-04 13:11:51.955:INFO:oxtjl.NotifyListener:main: Server started, you can now open http://localhost:8080/ in your browser to access your wiki.
2015-11-04 13:11:51.955:INFO:oxtjl.NotifyListener:main: ----------------------------------
2015-11-04 13:11:57,493 [XWiki initialization] INFO  .HibernateDataMigrationManager - Storage schema updates and data migrations are enabled 
2015-11-04 13:11:57,648 [XWiki initialization] INFO  .HibernateDataMigrationManager - No data migration to apply for wiki [xwiki] currently in version [72001] 
2015-11-04 13:11:57,648 [XWiki initialization] INFO  .HibernateDataMigrationManager - Checking Hibernate mapping and updating schema if needed for wiki [xwiki] 
2015-11-04 13:11:58,793 [XWiki Solr index job thread] INFO  o.x.s.s.i.j.IndexerJob         - Starting job of type [solr.indexer] with identifier [[solr, indexer]] 
2015-11-04 13:11:59,033 [XWiki Solr index job thread] ERROR o.x.s.s.i.j.IndexerJob         - Exception thrown during job execution 
java.lang.IllegalArgumentException: The resolver parameter doesn't contain an Entity Reference of type [SPACE]
	at org.xwiki.model.internal.reference.ExplicitReferenceEntityReferenceResolver.getDefaultReference(ExplicitReferenceEntityReferenceResolver.java:45) ~[xwiki-platform-model-7.3-milestone-2.jar:na]
	at org.xwiki.model.internal.reference.AbstractEntityReferenceResolver.resolveDefaultReference(AbstractEntityReferenceResolver.java:77) ~[xwiki-platform-model-7.3-milestone-2.jar:na]
	at org.xwiki.model.internal.reference.AbstractReferenceEntityReferenceResolver.resolve(AbstractReferenceEntityReferenceResolver.java:67) ~[xwiki-platform-model-7.3-milestone-2.jar:na]
	at org.xwiki.model.internal.reference.AbstractReferenceEntityReferenceResolver.resolve(AbstractReferenceEntityReferenceResolver.java:41) ~[xwiki-platform-model-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrEntityReferenceResolver.resolveMissingReference(SolrEntityReferenceResolver.java:173) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrEntityReferenceResolver.getSpaceReference(SolrEntityReferenceResolver.java:111) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrEntityReferenceResolver.getEntityReference(SolrEntityReferenceResolver.java:71) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrEntityReferenceResolver.resolve(SolrEntityReferenceResolver.java:63) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrEntityReferenceResolver.resolve(SolrEntityReferenceResolver.java:46) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrDocumentReferenceResolver.resolve(SolrDocumentReferenceResolver.java:48) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.reference.SolrDocumentReferenceResolver.resolve(SolrDocumentReferenceResolver.java:38) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.job.SolrDocumentIterator.next(SolrDocumentIterator.java:99) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.job.SolrDocumentIterator.next(SolrDocumentIterator.java:54) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.job.DiffDocumentIterator.next(DiffDocumentIterator.java:120) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.job.IndexerJob.updateSolrIndex(IndexerJob.java:113) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.search.solr.internal.job.IndexerJob.runInternal(IndexerJob.java:94) ~[xwiki-platform-search-solr-api-7.3-milestone-2.jar:na]
	at org.xwiki.job.internal.AbstractJob.runInContext(AbstractJob.java:209) [xwiki-commons-job-7.3-milestone-2.jar:na]
	at org.xwiki.job.internal.AbstractJob.run(AbstractJob.java:192) [xwiki-commons-job-7.3-milestone-2.jar:na]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_71]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_71]
	at java.lang.Thread.run(Thread.java:745) [na:1.7.0_71]
2015-11-04 13:11:59,033 [XWiki Solr index job thread] INFO  o.x.s.s.i.j.IndexerJob         - Finished job of type [solr.indexer] with identifier [[solr, indexer]]