title: Illegal string offset in array_map
body: <p>Try use function array_map</p>
  
  <pre><code> array_map(function ($items) {
                      return $items[$this-&gt;relatedKey];
                  }, $this-&gt;parseIds($ids))
  </code></pre>
  
  <p>$<code>ids</code> is array of item => value:</p>
  
  <pre><code> $ids = array:1 [
        "parent_id" =&gt; "15"
      ]
  </code></pre>
  
  <p>Key what need to find:</p>
  
  <pre><code>$this-&gt;relatedKey = "parent_id"
  </code></pre>
  
  <p>And get error:</p>
  
  <pre><code>Illegal string offset 'parent_id'
  </code></pre>
  
  <p>What I do wrong?</p>