Find all sites of a default class

Hi,
I'm trying to filter sites based on class names. According to documentation, The following code will return the class name
`mjcf_model.find_all('site')[0].dclass`
But instead, it returned an `MJCF Element`,
`mjcf_model.find_all('site')[0].dclass.dclass` will return the actual class name.
This makes filtering sites based on class names very ugly because sites with no default class names will return None, then doing
`mjcf_model.find('site','mysite').dclass.dclass` will result in errors.