Deserialize json when not include required field only gives error when the field is specified as null

[williamwyc]

I was looking into the change in this PR #861 , and I found that, it only throws error when you specify a required field in json with value null.
Let's say I have a DTO with field A as required, if i send json {"A":null}, it throws error as expected, but if I send json {}, which does not include our required field A, it does not throw error.
Should we throw error for both cases since the field is required?