Studio should show an error when mandatory vocabulary isn't selected

The issue appears when using a chainedDirectory or multiChainedDirectory widget. The vocabulary is marked mandatory, but studio does not check for that.

==== OLD DESC =====
This is a new issue for this customer.
Last week, the release process went OK
Today, the relase process is in errorno release created) with no apparent user error.

Fix the release creation process of the customer project