title: unexpected "=" in operand
body: <p>I am getting this error in a Hugo theme and have modified the code to use a simple example from the Hugo documentation and still get an error.</p>
  
  <blockquote>
    <p>unexpected "=" in operand</p>
  </blockquote>
  
  <p>Hugo Version</p>
  
  <blockquote>
    <p>Hugo Static Site Generator v0.40.1 linux/amd64 BuildDate: 2018-04-25T17:16:11Z</p>
  </blockquote>
  
  <p>Go Version</p>
  
  <blockquote>
    <p>go version go1.12 linux/amd64</p>
  </blockquote>
  
  <p>I have copied this code directly from the <a href="https://gohugo.io/functions/append/" rel="nofollow noreferrer">GoHugo - Append</a> example.</p>
  
  <p>Error</p>
  
  <pre><code>ERROR 2019/03/11 09:24:53 theme/partials/work.html : template: theme/partials/work.html:3: unexpected "=" in operand
  </code></pre>
  
  <p>Simplified Template</p>
  
  <pre><code>{{ partial "global-header.html" . }}
  
  {{ $s := slice "a" "b" "c" }}
  {{ $s = $s | append "d" "e" }}
  
  &lt;h1&gt;David&lt;/h1&gt;
  </code></pre>
  
  <p>I originally got the error in the <a href="https://themes.gohugo.io//theme/airspace-hugo/" rel="nofollow noreferrer">Hugo AirSpace</a> template at line 13 of the work.html partial.</p>
  
  <p>Sample Line</p>
  
  <pre><code>{{ $categories = $categories | append .category }}
  </code></pre>
  
  <p>Full Template</p>
  
  <pre><code>{{ partial "global-header.html" . }}
  
  &lt;!-- Portfolio Start --&gt;
  &lt;section id="portfolio-work"&gt;
      &lt;div class="container"&gt;
          &lt;div class="row"&gt;
            &lt;div class="col-md-12"&gt;
              &lt;div class="block"&gt;
                &lt;div class="portfolio-menu"&gt;
                  &lt;ul&gt;
                    {{ $categories := slice }}
                    {{ range .Site.Data.work.portfolio }}
                      {{ $categories = $categories | append .category }}
                    {{ end }}
                      &lt;li class="filter" data-filter="all"&gt;Everything&lt;/li&gt;
                    {{ range ( $categories | uniq ) }}
                      &lt;li class="filter" data-filter=".{{ . }}"&gt;{{ . }}&lt;/li&gt;
                    {{ end }}
                  &lt;/ul&gt;
                &lt;/div&gt;
                &lt;div class="portfolio-contant"&gt;
                  &lt;ul id="portfolio-contant-active"&gt;
                    {{ range .Site.Data.work.portfolio }}
                      &lt;li class="mix {{ .category }}"&gt;
                        &lt;a class="venobox" href="{{ $.Site.BaseURL }}{{ .image }}"&gt;
                          &lt;img class="img-responsive" src="{{ $.Site.BaseURL }}{{ .image }}" /&gt;
                          &lt;div class="overly"&gt;
                            &lt;div class="position-center"&gt;
                              &lt;i class="fa fa-search fz-20"&gt;&lt;/i&gt;
                              &lt;h2&gt;{{ .name }}&lt;/h2&gt;
                              &lt;p&gt;{{ .description }}&lt;/p&gt;
                            &lt;/div&gt;
                        &lt;/a&gt;
                    &lt;/li&gt;
                    {{ end }}
                  &lt;/ul&gt;
                &lt;/div&gt;
              &lt;/div&gt;
            &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/section&gt;
  
  &lt;!-- Clients Logo Section Start --&gt;
  &lt;section id="clients-logo-section"&gt;
    &lt;div class="container"&gt;
      &lt;div class="row"&gt;
        &lt;div class="col-md-12"&gt;
          &lt;div class="block"&gt;
            &lt;div id="clients-logo" class="owl-carousel"&gt;
              {{ range .Site.Data.work.clients }}
              &lt;div class="clients-logo-img"&gt;
                &lt;a href="{{ .url }}"&gt;&lt;img src="{{ $.Site.BaseURL }}{{ .image }}" alt="Features"&gt;&lt;/a&gt;
              &lt;/div&gt;
              {{ end }}
            &lt;/div&gt;
          &lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/section&gt;
  </code></pre>