Cvent Survey Response Results in `None`

Cvent-GetUpdate-Response.py

import suds
import os
url="https://api.cvent.com/soap/V200611.ASMX?WSDL"
client = suds.client.Client(url)
print(client)

login = client.factory.create('Login')

login.AccountNumber = os.environ['ACCOUNT_NUMBER']
login.UserName = os.environ['USER_NAME']
login.Password = os.environ['PASSWORD']

loginReponse = client.service.Login(
    os.environ['ACCOUNT_NUMBER'],
    os.environ['USER_NAME'],
    os.environ['PASSWORD']
)

sessionHeader = loginReponse._CventSessionHeader
session = client.factory.create('CventSessionHeader')
session.CventSessionValue = sessionHeader
client.set_options(
  soapheaders=(session)
)

getUpdated = client.factory.create('GetUpdated')

objectType = client.factory.create('GetUpdated.ObjectType')
# objectType.Event works fine.
# getUpdated.ObjectType.set(objectType.Event)
getUpdated.ObjectType.set(objectType.Response)
getUpdated.StartDate = '2019-04-01T00:00:00'
getUpdated.EndDate = '2020-04-06T00:00:00'
print(getUpdated)

guResponse = client.service.GetUpdated(
  getUpdated.ObjectType,
  getUpdated.StartDate,
  getUpdated.EndDate
)

print(guResponse) # Result: None

Here's an example result when it's switched to objectType.Event instead of response.

(GetUpdatedResult){
   Id[] = 
      "829F75E3-D148-4506-1BC4-123456789101",
...
 }