v0.17.3
This PR was created by Knope. Merging it will create a new release ### Fixes #### Remove spurious field_dict.update({}) for types without properties (#969) #### Fix invalid type check for nested unions Nested union types (unions of unions) were generating `isinstance()` checks that were not valid (at least for Python 3.9). Thanks to @codebutler for PR #959 which fixes #958 and #967. Co-authored-by: GitHub <github-actions@github.com>