Hi Oppia devs,
A new architecture for validating handler arguments is introduced in the codebase. If you plan to write new handlers make sure to write schema for all the request/payload arguments.
The guidelines for writing schemas are added in the wiki page (Writing schema for handler args).
For any discussion kindly contact, Rohit or Vojtech or Nikhil.
Nikhil (on behalf of the Data Handling Team)