{% if post.author %}
  {% assign author = post.author %}
{% elsif page.author %}
  {% assign author = page.author %}
{% else %}
  {% assign author = site.author %}
{% endif %}
{% if post.googleplus_user %}
    {% assign googleplus_user = post.googleplus_user | downcase %}
  {% elsif page.googleplus_user %}
    {% assign googleplus_user = page.googleplus_user | downcase %}
  {% else %}
    {% assign googleplus_user = site.googleplus_user | downcase %}
  {% endif %}
{% if author %}
  <span class="byline author vcard">Authored by <span class="fn">
  {% if !googleplus_user or googleplus_user == "ignore" %}
    {{ author }}
  {% else %}
    <a href="https://plus.google.com/{{ googleplus_user }}" rel="author">{{ author }}</a>
  {% endif %}
  </span></span>
{% endif %}

{% if post.author %}
  {% assign author = post.author %}
{% elsif page.author %}
  {% assign author = page.author %}
{% else %}
  {% assign author = site.author %}
{% endif %}
{% if post.googleplus_user %}
    {% assign googleplus_user = post.googleplus_user | downcase %}
  {% elsif page.googleplus_user %}
    {% assign googleplus_user = page.googleplus_user | downcase %}
  {% else %}
    {% assign googleplus_user = site.googleplus_user | downcase %}
  {% endif %}
{% if author %}
  <span class="byline author vcard">Authored by <span class="fn">
  {% if googleplus_user == "" or googleplus_user == nil or googleplus_user == "ignore" %}
    {{ author }}
  {% else %}
    <a href="https://plus.google.com/{{ googleplus_user }}" rel="author">{{ author }}</a>
  {% endif %}
  </span></span>
{% endif %}

Revert condition check to empty string check
Revert condition check to empty string check
