why get null from FormResponse in Google Forms?

Question

My GAS links to form. but it returns undefined(or null) from FormResponse. so why? Spreadsheet has response datas.

Setting information

• Trigger Source: From form Type: On form submit
• OAuth Scope https://www.googleapis.com/auth/forms

Code // is log. old version and V8.

function(e) {
  Logger.log(e) // FormResponse
  Logger.log(e.length) // undefined(V8:null)
  Logger.log(e.values) // undefined(V8:null)
  Logger.log(e.namedValues) // undefined(V8:null)
  Logger.log(e.items) // undefined(V8:null)
}