def _get(self, key, source, none=None, empty=None):
value = None
keys = self.map(key)
for key in keys:
value = source.get(key)
if value is not None:
break
if empty is not None and b9.empty(value):
return empty
elif none is not None and value is None:
return none
else:
return value
def empty(self, key):
return b9.empty(self.get(key))
