code: def _structure_default(self, obj, cl):
          
          if cl is Any or cl is Optional:
              return obj
          # We don't know what this is, so we complain loudly.
          msg = (
              "Unsupported type: {0}. Register a structure hook for "
              "it.".format(cl)
          )
          raise ValueError(msg)
docs: This is the fallthrough case. Everything is a subclass of `Any`.
  
          A special condition here handles ``attrs`` classes.
  
          Bare optionals end here too (optionals with arguments are unions.) We
          treat bare optionals as Any.