title: Error while using chatterbot
body: <p>I'm trying to make a simple QnA program using Python chatterbot.</p>
  
  <pre><code># -*- coding: utf-8 -*-
  from chatterbot import ChatBot
  
  bot = ChatBot(
      "SQLMemoryTerminal",
      storage_adapter='chatterbot.storage.SQLStorageAdapter',
      logic_adapters=[
          {
              "import_path": "chatterbot.logic.BestMatch",
              "statement_comparison_function": 
  "chatterbot.comparisons.levenshtein_distance"
          },
          {
              'import_path' : 'chatterbot.logic.LowConfidenceAdapter',
              'threshold' : 0.3,
              'default_response' : "Sorry. I can not find the exact answer."
          },
          'chatterbot.logic.multi_adapter.MultiLogicAdapter',
      ],
      input_adapter="chatterbot.input.TerminalAdapter",
      output_adapter="chatterbot.output.TerminalAdapter",
      read_only= True
  )
  
  print("input question")
  
  while True:
      try:
          print("Q : ",end="")
          bot_input = bot.get_response(None)
  
      except (KeyboardInterrupt, EOFError, SystemExit):
          break
  </code></pre>
  
  <p>However, when I try to use the multiadapter function built in chatterbot, I get an error.</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:/Users/KPvoice/PycharmProjects/Contact/ChatterbotTest.py", line 
  30, in &lt;module&gt;
      bot_input = bot.get_response(None)
    File "C:\Python36\lib\site-packages\chatterbot\chatterbot.py", line 113, 
  in get_response
      statement, response = self.generate_response(input_statement, 
  conversation_id)
    File "C:\Python36\lib\site-packages\chatterbot\chatterbot.py", line 132, 
  in generate_response
      response = self.logic.process(input_statement)
    File "C:\Python36\lib\site-packages\chatterbot\logic\multi_adapter.py", 
  line 52, in process
      output = adapter.process(statement)
    File "C:\Python36\lib\site-packages\chatterbot\logic\multi_adapter.py", 
  line  89, in process
      result.confidence = max_confidence
  AttributeError: 'NoneType' object has no attribute 'confidence'
  </code></pre>
  
  <p>I do not know how to solve it.</p>
  
  <p>The working environment is Windows 10, Python 3.7</p>