@Override
  public Object getVariable(String qname) {
    if (qname == null) {
      throw new NullPointerException(
        "Cannot get variable value for null qname");
    }
    final int pos = qname.indexOf(':');
    if (pos >= 0) {
      return getVariable(qname.substring(pos + 1),
                         getNamespace(qname.substring(0, pos)));
    }
    return getVariable(qname, Namespace.NO_NAMESPACE);
  }
@Override
  public Object getVariable(String qname)