title: How to delete all user names in DolphinDB?
body: <p>I am testing the user access control functionalities of DolphinDB database. As I quite often need to start all over again, I need to find a convenient way to delete all user names as an administrator. I have tried the following:</p>
  <pre><code>each(deleteUser, getUserList())
  </code></pre>
  <p>The idea is to use the template function &quot;each&quot; to apply &quot;deleteUser&quot; to each of the user names returned from function getUserList(). It returns the following error message:</p>
  <pre><code>Not allowed to create void vector
  </code></pre>
  <p>I don't quite understand why the script fails. Does someone have a clue?</p>