(dict-arg-default) Validation error at line 9 in recursive-type.webidl, inside `interface X -> operation recursive -> argument r`:
  undefined recursive(optional Recursive r);
                                         ^ Optional dictionary arguments must have a default value of `{}`.
(dict-arg-default) Validation error at line 10 in recursive-type.webidl, inside `interface X -> operation recursive2 -> argument f`:
  undefined recursive2(optional FriendX f);
                                        ^ Optional dictionary arguments must have a default value of `{}`.