Post History

Rails has a whole validation logic for showing nice errors whenever things are not valid. What you are adding an error to is the tags "field" of "Post" (in `app/models/post.rb` you will see a `has_many :tags`). Internally, rails also uses this information when you would programmatically check "which part of this post is invalid now?". You would ideally want that to answer to remain as "tags".

Perhaps the rails guide on validations can provide more information on alternative solutions: https://guides.rubyonrails.org/active_record_validations.html .