Comment 4 for bug 59249

There is a good reason to call the validate() method on field errors: we want to present all the validation errors to the user upfront, rather than have them fix the returned errors only to have new ones given on the next submission.

Using the branch edit form as an example, imagine that the user entered a value into the title field that caused a field validation error (e.g. they snuck in a new line character), and chose a branch name that was already in use. We'd want to display both errors to the user, which means invoking validate() even though we got a field validation error.