True, but in those cases the REST API should refuse the update with an explanatory message (it's a TODO to parse those exceptions and print them in a more user friendly way).

The CLI design too has some room for identifying for these types of things in the object model. Examples are the 'optional' and 'writeable' flags. However, they are not really implemented/honoured. That's OK though, taking the into account would improve the user experience, but ultimately the REST API is responsible for validating what the user sends. For example, if you create an object without writing a value for a non-optional field, the CLI will happily send it (although the optional flag is there), but the REST API will complain about the missing field.

I see this case in that category, what do you think?