Why set default value of dictionary parameters to None, but then change them to {} at beginning of method?

[derekmahar]

In several API methods like krakenex.api._query, why do you set the default value of some dictionary parameters to None, but then at the beginning of the method, immediately change None to the empty dictionary {}? Why not instead set the parameter default values to {}?

For example, why not replace

def _query(self, urlpath, data, headers=None, timeout=None):
        if data is None:
            data = {}
        if headers is None:
            headers = {}

with

def _query(self, urlpath, data={}, headers={}, timeout=None):

?

[veox]

Looks like an atavism, judging by commits 839b9a1 and 11ac129...