fix: date not json serializable

[madhavsh96]

My test case failed because of TypeError: Object of type date is not JSON serializable .

[maticardenas]

Hi @madhavsh96, thanks for the PR. Indeed, a date value in a schema section would raise an exception. I feel we should fix this in others parts too, and probably refactor this to have a proper method/function responsible of validating this.

I'm merging this for now and will open a follow-up improving this. Thanks!