title: SpannableStringBuilder append() NullPointerException
body: <pre><code>// Documentation from interface
  public SpannableStringBuilder append(CharSequence text) {
      int length = length();
      return replace(length, length, text, 0, text.length());
  }
  </code></pre>
  
  <p><code>SpannableStringBuilder</code> source code <code>append()</code> function doesn't avoid <code>NullPointerException</code>??
  If text is null, <code>append()</code> function definitely throw <code>NullPointerException</code>. 
  It's easily be forgotten to check every case if text is null. For example the text may from the server. 
  Anyone has a better idea for <code>SpannableStringBuilder</code> <code>append()</code> function to avoid npe?</p>