/// <summary>Adds a season number to the collection.</summary>
 /// <param name="season">The season number, which will be added.</param>
 /// <param name="watchedAt">An UTC datetime, when the season was watched.</param>
 /// <param name="episodes">A list of episode numbers. See also <see cref="PostHistoryEpisodes" />.</param>
 public void Add(int season, DateTime watchedAt, PostHistoryEpisodes episodes) => _seasons.Add(new PostHistorySeason(season, watchedAt, episodes));
 /// <summary>Adds a season number to the collection.</summary>
 /// <param name="season">The season number, which will be added.</param>
 /// <param name="episodes">A list of episode numbers. See also <see cref="PostHistoryEpisodes" />.</param>
 public void Add(int season, PostHistoryEpisodes episodes) => _seasons.Add(new PostHistorySeason(season, null, episodes));
 /// <summary>Initializes a new instance of the <see cref="PostHistorySeason" /> class.</summary>
 /// <param name="number">The number of this season.</param>
 /// <param name="watchedAt">An UTC datetime, when this season was watched.</param>
 /// <param name="episodes">>A list of episode numbers. See also <see cref="PostHistoryEpisodes" />.</param>
 public PostHistorySeason(int number, DateTime?watchedAt, PostHistoryEpisodes episodes)
 {
     Number    = number;
     WatchedAt = watchedAt;
     Episodes  = episodes;
 }