title: sqlalchemy can't get data with boolean field in filter option (specified with is)
body: <pre><code>Channel.query.filter(Channel.is_default == True).all()
  </code></pre>
  
  <p>When I use above expression it works,but an pep8 advice is occuered.So I use below expression instead.</p>
  
  <pre><code>Channel.query.filter(Channel.is_default is True).all()
  </code></pre>
  
  <p>But when I run the code, no data returned.And there is no error or warning.</p>