<footer class="bg-darkest py-6">
  <div class="container-lg px-4">
    <div class="col-lg-8 dim">
      <img src="{{ site.logo_file | absolute_url }}" alt="{{ site.title }}" class="float-left mr-4 dim">
      <p class="text-serif text-white text-small">&copy; Copyright 2016, under the terms of the MIT License. Created by <a href="//patrickmarsceill.com" class="text-white text-underline">Patrick&nbsp;Marsceill</a> in Philadelphia, USA.</p>
    </div>
  </div>
</footer>

<footer class="bg-darkest py-6">
  <div class="container-lg px-4">
    <div class="col-lg-8 dim">
      {% unless site.footer_logo_file == nil %}<img src="{{ site.footer_logo_file | absolute_url }}" alt="{{ site.title }}" class="float-left mr-4 dim">{% endunless %}
      <p class="text-serif text-white text-small">&copy; Copyright 2016, under the terms of the MIT License. Created by <a href="//patrickmarsceill.com" class="text-white text-underline">Patrick&nbsp;Marsceill</a> in Philadelphia, USA.</p>
    </div>
  </div>
</footer>

Add conditional to footer logo
Add conditional to footer logo
