fix bug

app/controllers/homework_commons_controller.rb

@@ -196,7 +196,7 @@ class HomeworkCommonsController < ApplicationController
       end
 
       if params[:format] == "xlsx"
-        complete_works = @work_excel.exist? ? @work_excel.where("work_status > 0").size : 0
+        complete_works = @work_excel.present? ? @work_excel.where("work_status > 0").size : 0
         if @user_course_identity >= Course::STUDENT
           tip_exception(403, "无权限操作")
         elsif complete_works == 0
@@ -216,7 +216,7 @@ class HomeworkCommonsController < ApplicationController
         if @user_course_identity >= Course::STUDENT
           tip_exception(403, "无权限操作")
         else
-          if @work_excel.exist?
+          if @work_excel.present?
             zip_works = @work_excel&.where("work_status > 0")
             status = checkfileSize(zip_works)
           else