title: Override lxml behavior to write a closing and opening element for Null tags
body: <pre><code>root = etree.Element('document')
  rootTree = etree.ElementTree(root)
  firstChild = etree.SubElement(root, 'test')
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>&lt;document&gt;
  &lt;test/&gt;
  &lt;/document
  </code></pre>
  
  <p>I want the output to be:</p>
  
  <pre><code>&lt;document&gt;
  &lt;test&gt;
  &lt;/test&gt;
  &lt;/document&gt;
  </code></pre>
  
  <p>I know both are equivalent but is there a way to get the output that i want .</p>