How to reproduce:

• In a content type's view (metadata-set), add a fieldset without name.
• Add 2 references to the same attribute (metadata-ref) in this unamed fieldset
• Start your application
  • A Configuration should be thrown to explain that it's not possible to reference an attribute more than once => OK
  • But the message of this error tries to display the name of the fieldset.
  • This leads to another error because the fieldset has no name... => KO