When Updating a metadata instance to remove a value from a specific instance, currently today the API fails if the field has no value.

I would like to propose that if the field had a value it is removed, and if it doesn't - then just ignore the operation. Similar to what add does if the field already has a value, it just silently replaces it.

As an option, in case others are relying on the failure, maybe add a new operation "forceRemove" so that if there is no value, the code will just ignore it and continue with the other updates.