Ahh. That makes sense then. The value of the key being optional is indeed a different concept. Fwiw, this is one huge downside of Swagger APIs. Swagger supports the concept of optional keys but not optional values &gt;.&gt;<p>I have yet to find a validation library that supports all the sorts of things I expect it to. One place they tend to fail is the ways they can fulfill default values.<p>Say a field has an error and I want to just give it a default value when it&#x27;s broken? That particular feature doesn&#x27;t exist in any library i&#x27;ve found so far (for python) =&#x2F;<p>Granted, this sort of blends into the usual &quot;It&#x27;s a validation library not a serialization library&quot;. But they all make a half-assed attempt at the other side in my experience.