STAC Item support with null geometry

[kalxas]

Description

STAC Item spec says that geometry can be null and bbox is required if geometry is null.
https://github.com/radiantearth/stac-spec/blob/master/item-spec/item-spec.md

Test with a copy of https://github.com/radiantearth/stac-spec/blob/master/examples/simple-item.json
with no bbox and "geometry": null, throws the following error:

Error message
=========
Could not parse "/tmp/metadata" as an XML record

Traceback (most recent call last):

  File "/home/pycsw/pycsw/pycsw/core/admin.py", line 370, in load_records

    record = metadata.parse_record(context, metadata_record, repo)

  File "/home/pycsw/pycsw/pycsw/core/metadata.py", line 120, in parse_record

    return _parse_metadata(context, repos, record)

  File "/home/pycsw/pycsw/pycsw/core/metadata.py", line 135, in _parse_metadata

    return [_parse_json_record(context, repos, record)]

  File "/home/pycsw/pycsw/pycsw/core/metadata.py", line 1632, in _parse_json_record

    recobj = _parse_stac_item(context, repos, record)

  File "/home/pycsw/pycsw/pycsw/core/metadata.py", line 1751, in _parse_stac_item

    _set(context, recobj, 'pycsw:BoundingBox', util.bbox2wktpolygon(util.geojson_geometry2bbox(record['geometry'])))

  File "/home/pycsw/pycsw/pycsw/core/util.py", line 185, in geojson_geometry2bbox

    geom_type = geometry.get('type')

AttributeError: 'NoneType' object has no attribute 'get' 

Environment

• operating system:
• Python version:
• pycsw version:
• source/distribution
  • git clone
  • DebianGIS/UbuntuGIS
  • PyPI
  • zip/tar.gz
  • other (please specify): Docker (latest)
• web server
  • Apache/mod_wsgi
  • CGI
  • other (please specify):

[tomkralidis]

Looking at the STAC Item spec, I am interpreting the inverse (if geometry is not null, bbox is required), so that bbox provides a simple minimum bounding geometry if geometry is defined.

Having said this, I've reproduced the error and applied a fix as part of #991.