Merge pull request #49 from Sander0542/fix/subscription

Fix Subscription@SubscribedAt

Author: jensenkd

Source/Plex.ServerApi/PlexModels/Account/Subscription.cs

@@ -10,7 +10,7 @@ public class Subscription
         public bool Active { get; set; }
 
         [JsonPropertyName("subscribedAt")]
-        public DateTime SubscribedAt { get; set; }
+        public DateTime? SubscribedAt { get; set; }
 
         [JsonPropertyName("status")]
         public string Status { get; set; }