more information in the logs when errors during the import + import asset collections without custom fields

app/controllers/admin/imports_controller.rb

@@ -32,7 +32,7 @@ module Admin
 
         redirect_to Locomotive.config.delayed_job ? admin_import_url : new_admin_import_url
       rescue Exception => e
-        logger.error "[Locomotive import] #{e.message}"
+        logger.error "[Locomotive import] #{e.message} / #{e.backtrace}"
 
         @error = t('errors.messages.invalid_theme_file')
         flash[:alert] = t('flash.admin.imports.create.alert')

lib/locomotive/import/asset_collections.rb

@@ -37,6 +37,8 @@ module Locomotive
       end
 
       def add_or_update_fields(asset_collection, fields)
+        return if fields.blank?
+
         fields.each_with_index do |data, position|
           name, data = data.keys.first, data.values.first