Allow null geometry to align with STAC and Features
PR Checklist:
[x] This PR has no breaking changes.
[x] This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
[x] I have added my changes to the CHANGELOGor a CHANGELOG entry is not required.
Related Issue(s):
430
Proposed Changes:
PR Checklist:
stac-specdirectory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)