fix for image destroy

app/controllers/ps_admin/image_controller.rb

@@ -80,9 +80,13 @@ module PsAdmin
       image = Image.where(id: params[:id]).first
       unless image.blank?
         if image.cover.eql?(true)
-          img = Image.where('imageable_type = ? AND imageable_id = ? AND id != ?', image.imageable_type, image.imageable_id, image.id).first
-          img.cover = true
-          img.save
+          img = Image.by_image_type(image.imageable_type)
+                     .where('imageable_id = ? AND id != ?',
+                            image.imageable_id, image.id).first
+          unless img.blank?
+            img.cover = true
+            img.save
+          end
         end
         image.destroy
       end