During the integration of the new way of configuring content blocks in Essentials, I noticed an ERROR log message from the CMS Content Type Service. I debugged this with Ate, and we found that the hipposysedit:field node which represents the copntent blocks field in the nodetype definition (/hippo:namespaces/<project>/<docType>/hipposysedit:nodetype/hipposysedit:nodetype) has the jipposysedit:type property set to "nt:base". Because this is an abstract node type, the Content Type Service doesn't like this and throws an ERROR. We found a workaround: Use "hippo:compound" instead. This is not 100% correct, as for example hippo:mirror or hippostd:html do not extend from hippo:compound, but it works, and the ERROR is gone. Essentials will use "hippo:compound". I suggest to update the documentation and demo project of content blocks to also use hippo:compound. I'll also log an issue on the Content Type Service.