PlayerInfo constructor Null safety
- {DurationInformation? durationInformation,
 - DifficultyInformation? difficultyInformation,
 - int? minutesPlayed,
 - int? questionsAnswered,
 - int? elo,
 - int? questionsRightAnswered,
 - CategoryInformation? categoryInformation,
 - String? username}
 
Implementation
PlayerInfo(
    {this.durationInformation,
      this.difficultyInformation,
      this.minutesPlayed,
      this.questionsAnswered,
      this.elo,
      this.questionsRightAnswered,
      this.categoryInformation,
      this.username});