docs: public static CompletionStage<Void> allOf(CompletionStage<Void> first, CompletionStage<Void> second) {
        if (!isCompletedSuccessfully(first)) {
           if (isCompletedSuccessfully(second)) {
              return first;
           } else {
              return CompletionStages.aggregateCompletionStage().dependsOn(first).dependsOn(second).freeze();
           }
        }
        return second;
     }