BUG: support writing None geometries (for geopackage files)

[theroggy]

At least in geopackages, it is valid to have NULL/None geometries in a layer.

However, when writing a GeoDataFrame with a None geometry this throws an error. Depending if the None geometry is first in the GeoDataframe or not triggers another error.

The following code triggers the errors:

import geopandas as gpd
import pyogrio
import shapely.geometry

# This results in ValueError: geometry_type must be provided
output_path = r"C:\temp\test_none_geom.gpkg"
test_gdf = gpd.GeoDataFrame(
        geometry=[
                None,
                shapely.geometry.Polygon(shell=[(1, 1), (1, 2), (2, 2), (2, 1), (1, 1)])],
        crs="epsg:31370")
pyogrio.write_dataframe(test_gdf, output_path)

# This results in TypeError: cannot convert 'NoneType' object to bytearray
test_gdf = gpd.GeoDataFrame(
        geometry=[
                shapely.geometry.Polygon(shell=[(1, 1), (1, 2), (2, 2), (2, 1), (1, 1)]),
                None],
        crs="epsg:31370")
pyogrio.write_dataframe(test_gdf, output_path)

[brendan-ward]

We took a fairly strict view when building this out that geometries must always be present, and didn't add adequate handling for when they aren't. I'm assuming that GDAL/OGR can handle NULL geometries provided we construct things that way, so we should allow this - and allow GDAL/OGR to be the gatekeeper if those aren't valid for a particular data format.

[theroggy]

reference #105