Outputs invalid GeoJSON for null geometries

[danvk]

If you set geometry to None in a Feature, it gets dropped from the feature during serialization:

>>> import pygeojson
>>> pygeojson.dumps(pygeojson.Feature(id="123", geometry=None))
'{"type": "Feature", "id": "123", "properties": {}}'

This is in violation of the spec, which states that a Feature must have a geometry member, which may be null.

I noticed that pygeojson has a test for reading null geometries, but no test for writing them back:

pygeojson/tests/test_pygeojson.py

Lines 54 to 58 in eaf554e

	def test_feature_with_null_geom(load_json):
	o: Feature = load_json("feature_with_null_geom.json")
	assert o == Feature(
	id=None, bbox=None, type="Feature", geometry=None, properties={},
	)