No, the domain of URIs does not have *any* concept of a null value.  It only has the concept of a string being empty or not empty (or the key not existing at all...ie: it doesn't exist in your params dict).

You are trying to map a Python concept (the singleton object None, which is used for a variety of purposes) into a domain that does not have an equivalent concept.

That said, following the requests model of omitting the key if the value is None is something we could consider as a convenience enhancement.  But we would again run into Python's strict backward compatibility policy.  I could imagine some programmer building an internal web service that turns the string 'None' back into a Python None value.  The fact that it would have to be an internal thing would mean we'd never hear about it...until we broke it :)

Whether or not adding this feature would require a new keyword argument to urlencode is a judgment call.  It might be an acceptable change in a feature release.