If I do:

union Question = QuestionMultipleChoice | QuestionText | QuestionNumber
union NewQuestionResult = Question | WrongToken

I get an error Union type NewQuestionResult can only include Object types, it cannot include Question., while:

union Question = QuestionMultipleChoice | QuestionText | QuestionNumber
union NewQuestionResult = QuestionMultipleChoice | QuestionText | QuestionNumber | WrongToken

works… But this leads to 2 questions:

1. why on earth would one fordid Unions of Unions? ML languages have been doing this for years without any issue.
2. how can I avoid the very dangerous code duplication it creates? Here I just have 2 lines to maintain, but I will surely run into troubles if for any single function that may return a Question or some errors I need to create a new line. The schema will be impossible to maintain in a few days!

MWE:

type QuestionMultipleChoice {
  question: String
  nbChoices: Int!
}

type QuestionText {
  question: String
}

type QuestionNumber {
  question: String
}

type WrongToken {
  _: Boolean
}

union Question = QuestionMultipleChoice | QuestionText | QuestionNumber

union NewQuestionResult = Question | WrongToken

type Mutation {
  newQuestion: NewQuestionResult
}

type Query {
  hello: String
}