private void configurationElement(XNode context) {
    try {
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.isEmpty()) {
        // 如果 namespace 不存在会直接抛出异常
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      
      // ... ...
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
    }
  }