title: elixir - how to add conditional pipe into pipeline?
body: <p>I have a small pipeline in elixir, it's about changing <code>ecto</code> model state:</p>
  
  <pre><code>model
  |&gt; cast(params, ~w(something), ~w())
  |&gt; conditional
  |&gt; Repo.update
  </code></pre>
  
  <p>The problem is that I have <code>conditional</code> pipe which can be nil sometimes, so in the case it's nil it should do nothing and can works (I presume it will be <code>fn(x) -&gt; x end</code>)</p>
  
  <p>So, my question is: "how can I do that"?</p>