Mark guild as optional for invite

src/Discord.Net.Core/Entities/Invites/IInvite.cs

@@ -19,7 +19,7 @@ namespace Discord
         /// <summary> Gets the guild this invite is linked to. </summary>
         IGuild Guild { get; }
         /// <summary> Gets the id of the guild this invite is linked to. </summary>
-        ulong GuildId { get; }
+        ulong? GuildId { get; }
         /// <summary> Gets the name of the guild this invite is linked to. </summary>
         string GuildName { get; }
         /// <summary> Gets the approximated count of online members in the guild. </summary>

src/Discord.Net.Rest/API/Common/Invite.cs

@@ -8,7 +8,7 @@ namespace Discord.API
         [JsonProperty("code")]
         public string Code { get; set; }
         [JsonProperty("guild")]
-        public InviteGuild Guild { get; set; }
+        public Optional<InviteGuild> Guild { get; set; }
         [JsonProperty("channel")]
         public InviteChannel Channel { get; set; }
         [JsonProperty("approximate_presence_count")]

src/Discord.Net.Rest/Entities/Invites/RestInvite.cs

@@ -14,7 +14,7 @@ namespace Discord.Rest
         public int? PresenceCount { get; private set; }
         public int? MemberCount { get; private set; }
         public ulong ChannelId { get; private set; }
-        public ulong GuildId { get; private set; }
+        public ulong? GuildId { get; private set; }
         internal IChannel Channel { get; private set; }
         internal IGuild Guild { get; private set; }
 
@@ -35,9 +35,9 @@ namespace Discord.Rest
         }
         internal void Update(Model model)
         {
-            GuildId = model.Guild.Id;
+            GuildId = model.Guild.IsSpecified ? model.Guild.Value.Id : default(ulong?);
             ChannelId = model.Channel.Id;
-            GuildName = model.Guild.Name;
+            GuildName = model.Guild.IsSpecified ? model.Guild.Value.Name : null;
             ChannelName = model.Channel.Name;
             MemberCount = model.MemberCount.IsSpecified ? model.MemberCount.Value : null;
             PresenceCount = model.PresenceCount.IsSpecified ? model.PresenceCount.Value : null;