Voluptuous double validate trick

gistfile1.txt

# schema as follows, currently:
>>> schema = Schema({'logging': {Required('file_level', default='info'): str, 
...                              Required('console_level', default='info'): str}})

# this works as desired:                            
>>> schema({'logging': {'file_level': 'warning'}})
{'logging': {'file_level': 'warning', 'console_level': info'}}

# this doesn't:
>>> schema({}})
{}

# what's the recommended way to have this happen:
>>> schema({}})
{'logging': {'file_level': 'info', 'console_level': info'}}

schema = Schema({Required('logging', default=PopulateWithDefaults({})): {Required('file_level', default='info'): str,
                              Required('console_level', default='info'): str}})

?

schema = Schema({Required('logging', default=Populate({})): {
                                   Required('file_level', default='info'): str,
                                   Required('console_level', default='info'): str
}})