新手问题： 上传图片为空时，update 方法返回成功。 选择上传图片后提交出现问题：

request:

schema.rb:

Gemfile:

以下为代码：
model：

class Compressor < ApplicationRecord
  has_attached_file :image, styles: { medium: "300x300>" thumb: "100x100> "}, default_url: "/images/:style/missing.png"
  validates_presence_of :image
  validates_attachment_content_type :image, content_type: /\Aimage\/.*\Z/
end

controller:

class CompressorsController < ApplicaitionController
  before_action :set_compressor, only: [:show, :edit, :update, :destroy ]
  def create
    @compressor = Compressor.new(compressor_params)
    respond_to do |format|
      if @compressor.save
        format.html { redirect_to @compressor, notice: "成功！"}
      else
        format.html { render :edit }
      end
    end
  end

  private

  def set_compressor
    @compressor = Compressor.find(params[:id])
  end

  def compressor_params
    params.require(:compressor).permit(:mj_no, :drawing_no, :apply, :year_start, :year_end, :oe_no, :brand, :capacity, :voltage, :refrigerant, :oe_type, :mj_type, :grooves, :pulley_dia, :price, :image)
  end

end