title: getSupportActionBar() NullPointerException
body: <p>In <code>onCreate()</code> method of activity I have this code for <code>ToolBar</code>:</p>
  
  <pre><code>toolbar = (Toolbar) findViewById(R.id.tool_bar);
  setSupportActionBar(toolbar);
  getSupportActionBar().setDisplayHomeAsUpEnabled(true);
  </code></pre>
  
  <p>My IDE warms me that <code>getSupportActionBar().setDisplayHomeAsUpEnabled(true);</code> may produce <strong><em><code>NullPointerException</code></em></strong>. </p>
  
  <p><strong><em>My question is should I ignore it and how can I fix it anyway?</em></strong></p>