title: File exists and IS directory, but listFiles() returns null
body: <p><a href="http://developer.android.com/reference/java/io/File.html#listFiles%28%29">The documentation for <code>File.listFiles()</code></a> suggests that <code>null</code> will ONLY be returned in the case that the file calling it is not a directory.</p>
  
  <p>I have the following:</p>
  
  <pre><code>String dir = "/storage/emulated/0";
  File f = new File(dir);
  Log.v("Files",f.exists()+"");
  Log.v("Files",f.isDirectory()+"");
  Log.v("Files",f.listFiles()+"");
  </code></pre>
  
  <p>The log reads:</p>
  
  <pre><code>true
  true
  null
  </code></pre>
  
  <p>For some reason, <code>listFiles(</code>) is returning <code>null</code> even though the <code>File</code> is recognized as a valid directory. I'm not super familiar with Android file hierarchy behavior, so I would guess the problem lies in there.</p>
  
  <p>For reference, I'm debugging on my Moto X, and results are the same whether the phone is plugged in to my computer or not - so I don't think it has to do with mounting when plugged in.</p>