Terraform v0.14.0 introduced a new experimental language feature for declaring object type constraints with optional attributes in your module's input variables. Thanks to feedback from those who tried the experiment, a refinement of that functionality is now stablized in Terraform v1.3.
https://www.terraform.io/language/upgrade-guides#concluding-the-optional-attributes-experiment
Full Changelog: v1.0.0...v2.0.0