text: Title: Error: Warning! Status check on the deployed lambda failed. A GET request to '/' yielded a 502 response code.
  Body: <!--- Provide a general summary of the issue in the Title above -->
  ## Context
  When im trying to deploy using _zappa update dev_ im getting this error:
  
  Error: Warning! Status check on the deployed lambda failed. A GET request to '/' yielded a 502 response code.
  
  ## Expected Behavior
  Could not get a valid link such as https://**********.execute-api.us-west-2.amazonaws.com/dev such as this
  
  ## Actual Behavior
  `{'message': 'An uncaught exception happened while servicing this request. You can investigate this with the `zappa tail` command.', 'traceback': ['Traceback (most recent call last):', ' File /var/task/handler.py, line 540, in handler with Response.from_app(self.wsgi_app, environ) as response:', ' File /var/task/werkzeug/wrappers/base_response.py, line 287, in from_app return cls(*_run_wsgi_app(app, environ, buffered))', ' File /var/task/werkzeug/wrappers/base_response.py, line 26, in _run_wsgi_app return _run_wsgi_app(*args)', ' File /var/task/werkzeug/test.py, line 1119, in run_wsgi_app app_rv = app(environ, start_response)', TypeError: 'NoneType' object is not callable]}`
  
  when im trying to access any endpoint from my application
  
  ## Your Environment
  <!--- Include as many relevant details about the environment you experienced the bug in -->
  * Zappa 0.54.1
  * Python version 3.7
  * Zappa settings
  {
      "dev": {
          "app_function": "app.app",
          "aws_region": "us-west-2",
          "profile_name": "default",
          "project_name": "***************",
          "runtime": "python3.7",
          "s3_bucket": "zappa-*********"
      }
  }
  