如何访问Rails的'不能为空'错误消息？

class ApplicationController< ActionController::Base
  rescue_from ActiveRecord::RecordInvalid, with: :render_record_invalid_error

  private

  def render_record_invalid_error(exception)
    @error_message = exception.record.errors.full_messages.join(", ")
    render json: { error: @error_message }, status: :unprocessable_entity
  end
end

class User< ApplicationRecord
  validates :name, presence: true
end

user = User.new
user.valid?
user.errors.full_messages # 获取错误消息

<%= form_with(model: user) do |form| %>
  <%= form.label :name %>
  <%= form.text_field :name %>
  <% if user.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(user.errors.count, "error") %> prohibited this user from being saved:</h2>
      <ul>
      <% user.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>
  <%= form.submit %>
<% end %>