title: catching classes that do not inherit from BaseException is not allowed
body: <p>I'm making a custom plugin to query a database for user info to aide customer support.  My backend is slack.</p>
  
  <p>Everytime I start the bot command I'm greeted with:</p>
  
  <pre><code>Computer says nooo. See logs for details:
  catching classes that do not inherit from BaseException is not allowed
  </code></pre>
  
  <p>I'm not sure if this is warning me that I'm attempting to catch an exception that isn't a BaseClass in my code or if an unknown exception was raised and caught elsewhere outside of my plugin.</p>
  
  <p>To debug I tried:</p>
  
  <pre><code>try:
      do_the_thing()
  except (TypeError, ValueError) as e:
      return('Something went wrong.')
  </code></pre>
  
  <p>I also tried:</p>
  
  <pre><code>try:
      do_the_thing()
  except Exception as e:
      return('Something went wrong.')
  </code></pre>
  
  <p>And I still get the errbot admonition.  Note that the command still runs and does the right thing where there is no exception raised by do_the_thing().</p>