Studio fails to build the jar when a subworkflow id is not provided

Have a workflow, say MyWF.
It has a subworkflow. But the user just dropped the subworkflow and did not enter the subworflow id. The use saves MyWF.
The Studio can then no more build the .jar:

• At runtime, when updating the server:
  • The chasing arrows run indefinitely in the browser
  • The log reports:

    Invalid package - no package.xml file found in package irs-poc-0.0.0-SNAPSHOT-1361808997
    

    Full line (there are no other reported error):

    13-09-05 08:26:37,631 ERROR [ConnectDownloadThread-1-1] [org.nuxeo.connect.downloads.LocalDownloadingPackage] org.nuxeo.connect.update.PackageException: Invalid package - no package.xml file found in package irs-poc-0.0.0-SNAPSHOT-1361808997
    

• It was the missing subworkflow id, because in Studio, when you want to tag your version you have this alert:

  https://connect.nuxeo.com
  uncaught Exception: Failed to build feature with type 'workflow' and id "MyWF'