private void addUser(String name, String phone) throws PersistenceException {
    if (userExists(name)) {
      throw new IllegalArgumentException("A number for " + name + " already exists.");
    }
    updateUser(name, phone);
  }
The view data store.
<code>null</code> indicates that the view properties should be used instead of the data store.
ambari-views/examples/phone-list-view/src/main/java/org/apache/ambari/view/phonelist/PhoneListServlet.java