TypeError fix when using empty `refresh_token_params`.
Fixes
@@ -206,6 +206,7 @@ class OAuth2Session(Session):
:return: A :class:`OAuth2Token` object (a dict too).
"""
refresh_token = refresh_token or self.token.get('refresh_token')
+ if self.refresh_token_params is not None:
kwargs.update(self.refresh_token_params)
body = prepare_token_request(
