title: typehints -> None or leave blank
body: <p>Using python 3, one has the option to use typehints. </p>
  
  <p>My question is, if a function returns None, should one add this, or leave it blank.</p>
  
  <p>i.e.</p>
  
  <pre><code>def hint(p:str) -&gt; None:
      pass
  
  def no_hint(p:str):
      pass
  </code></pre>
  
  <p>And which PEP addresses this?</p>