If you get this model error message, an action has been orphaned in your model. For example a Class has been deleted, but for some reason the class action belonging to it was left behind.

To remove actions without a name, open the OCL debugger for the model itself by right clicking on a diagram background and selecting Extras -> Open model debugger...

• Make one (probably the only one) of the expressions there an Action (1)

• Paste the code below (2)

• Execute it using F5 or the button (3)

AbstractAction.allInstances->select(aa|aa.Name.isNullOrEmpty).delete

Close the dialog and save your model as usual.