apollo-ios: Compile error of generated code with 0.17.0

Looks like we lost empty dictionary literals somewhere.

Query. Clearly has {} which seems to be the issue trigger.

/// query ExplicitPreferenceCompanionQuestions {
  ///   ExplicitPreferences_personalizationQuestions(request: {}) {
  ///     __typename
  ///     companionsQuestion {
  ///       __typename
  ///       selected
  ///     }
  ///   }
  /// }