Handle union return types

[Ludo978]

I have requests that can have 2 return types using union.
Example:

union SuccessOrError = GraphqlError | Success

mutation deleteAccount($accountId: String!) {
  deleteAccount(accountId: $accountId) {
      ... on Success {
          success
          message
      }
      ... on GraphqlError {
          success
          message
          code
      }
  }
}

Dociql displays that:

{
  "data": {}
}

I tried to expand fields without success.
Do you have an idea of how can I make it works?