message: Removed warning in ir solver
  Removed the warning in the ir solver by providing a `nullptr` as the
  default value for the factory created parameter `criteria`.
diff: @@ -122,7 +122,7 @@ public:
  * Criterion factories.
  */
  std::vector<std::shared_ptr<const stop::CriterionFactory>>
  - GKO_FACTORY_PARAMETER(criteria);
  + GKO_FACTORY_PARAMETER(criteria, nullptr);
  /**
  * Inner solver factory.
  