使用PYTHON Wit.ai如果traits：TypeError中没有trait，则不能迭代类型为'NoneType'的参数

如何解决使用PYTHON Wit.ai如果traits：TypeError中没有trait，则不能迭代类型为'NoneType'的参数

def first_trait_value(traits,trait):
  """
  Returns first trait value
  """
  if trait not in traits:
    return None
  val = traits[trait][0]['value']
  if not val:
    return None
return val

从Facebook页面输入消息时出现错误。但是当我把信息手册放进去的时候。没有错误发生。上面是那个功能。

def message_form_entity(msg):
  response = None
  entity,trait,value = wit_response(msg)
  greeting = first_trait_value(trait,'wit$greetings')
  sentiment = first_trait_value(trait,'wit$sentiment')
  course = first_trait_value(trait,'wit_course')
  print(sentiment,greeting,course)
  if greeting:
    response = "{}! \nwelcome suza bot.\ncan I help you ?".format(str(value))
  elif entity == 'closes:closes':
    response = "{} :) \n you are welcome".format(str(value))
  elif course:
    response = "PhD in Kiswahili. \n Masters of Chemistry. \nMasters of  Science in Environmental Science. \nDegree of Science in Environmental Health. \nBachelor Degree of information Application and Management. \nBachelor Degree of Arts in Geography and Environmental Studies."
#     # response = random.choice(resp) 
  elif sentiment:
    response = 'Glad you liked it.' if sentiment == 'positive' else 'Hmm.' 
  if response == None:
    response = 'sorry not understand this'

  return (response)