Fix: do not require empty data dict for create()

[nejch]

There's a quirk in the CreateMixin when checking for required attributes in _check_missing_create_attrs, which requires a data dict. But some create methods don't require additional data, e.g. if the only required attribute is already provided by their parent manager id (e.g. for project export, see https://docs.gitlab.com/ee/api/project_import_export.html).

This means the docs are sometimes asking people to pass an empty dict which I think is confusing for newcomers (and maybe unpythonic?).

This small fix allows using create() without passing a dict. The UpdateMixin is doing something similar with new_data = new_data or {} but I thought this is a bit more explicit with None.

I didn't add any checks as the data is already validated in _check_missing_create_attrs based on each Manager's _create_attrs and is already tested (see below), so I hope I covered everything :)

python-gitlab/gitlab/tests/test_mixins.py

Lines 265 to 276 in e5afb55

	def test_create_mixin_missing_attrs(self):
	class M(CreateMixin, FakeManager):
	_create_attrs = (("foo",), ("bar", "baz"))
	mgr = M(self.gl)
	data = {"foo": "bar", "baz": "blah"}
	mgr._check_missing_create_attrs(data)
	data = {"baz": "blah"}
	with self.assertRaises(AttributeError) as error:
	mgr._check_missing_create_attrs(data)
	self.assertIn("foo", str(error.exception))

.

[max-wittig]

You're right. This was kinda unpythonic before. Thanks for the change!