title: "Missing 1 required positional argument: 'resp'" when invoking Falcon resource responder that has a 'self' argument
body: <p>I am developing a WSGI application on Windows. I use peewee (which is supposedly unrelated) and:</p>
  
  <pre><code>falcon==2.0.0
  waitress==1.4.3
  </code></pre>
  
  <p>I have the following code in my <code>resources.py</code>:</p>
  
  <pre class="lang-py prettyprint-override"><code>from models import Board
  
  class BoardResource:
      def on_get_collection(self, req, resp):
          resp.media = Board.select()
  
      def on_get(self, req, resp):
          code = req.get_param('code')
          resp.media = Board.get_by_id(code)
  </code></pre>
  
  <p>I have the following code in my <code>app.py</code>:</p>
  
  <pre class="lang-py prettyprint-override"><code>import falcon
  import models
  from resources import BoardResource
  
  def init():
      models.init()
      api = falcon.API()
      api.add_route('/boards', BoardResource, suffix='collection')
      api.add_route('/board', BoardResource)
      return api
  
  api = init()
  </code></pre>
  
  <p>I start the app with this command: <code>waitress-serve app:api</code>. When I request <code>/boards</code> from the API, I get this error:</p>
  
  <pre><code>ERROR:waitress:Exception while serving /boards
  Traceback (most recent call last):
    File "c:\users\pepsiman\.virtualenvs\hsech-api\lib\site-packages\waitress\channel.py", line 349, in service
      task.service()
    File "c:\users\pepsiman\.virtualenvs\hsech-api\lib\site-packages\waitress\task.py", line 169, in service
      self.execute()
    File "c:\users\pepsiman\.virtualenvs\hsech-api\lib\site-packages\waitress\task.py", line 439, in execute
      app_iter = self.channel.server.application(environ, start_response)
    File "c:\users\pepsiman\.virtualenvs\hsech-api\lib\site-packages\falcon\api.py", line 269, in __call__
      responder(req, resp, **params)
  TypeError: on_get_collection() missing 1 required positional argument: 'resp'
  </code></pre>
  
  <p>I decided to remove the <code>self</code> argument from the definiton of <code>on_get_collection</code> and the error was gone. I know that <code>self</code> must be there and have no idea why it doesn't work like that. Any ideas how to fix?</p>