AjaxLink<Object> button = new AjaxLink<Object>( "editLocationButton" ) {

  private static final long serialVersionUID = 1L;

  public void onClick( AjaxRequestTarget p_target ) {
    // do things
  }

  /**
   * @see org.apache.wicket.markup.html.link.AbstractLink#isLinkEnabled()
   */
  @Override
  protected boolean isLinkEnabled() {
    return super.isLinkEnabled() && getSelectedLocation() != null;
  }
};

<td style="width:0%">
                <a href="#" wicket:id="editLocationButton" class="editButton iconButton">
                    <wicket:message key="button.edit.location"></wicket:message>
                </a>
            </td>

<td style="width:0%">
    <span class="editButton iconButton" id="editLocationButton7b6"><em>

    </em></span>
</td>