ction>
    <section class="desc markdown">
      <p>Get the first key in the map. Returns <code>null</code> if the map is empty.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class="language-dart">K firstKey() {
  if (_root == null) return null;
  return _first.key;
}</code></pre>
    </section>

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