Initial fix (#1160)

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

@@ -0,0 +1,10 @@
+using Newtonsoft.Json;
+
+namespace Discord.API
+{
+    public class InviteVanity
+    {
+        [JsonProperty("code")]
+        public string Code { get; set; }
+    }
+}

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -929,13 +929,13 @@ namespace Discord.API
             }
             catch (HttpException ex) when (ex.HttpCode == HttpStatusCode.NotFound) { return null; }
         }
-        public async Task<InviteMetadata> GetVanityInviteAsync(ulong guildId, RequestOptions options = null)
+        public async Task<InviteVanity> GetVanityInviteAsync(ulong guildId, RequestOptions options = null)
         {
             Preconditions.NotEqual(guildId, 0, nameof(guildId));
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
-            return await SendAsync<InviteMetadata>("GET", () => $"guilds/{guildId}/vanity-url", ids, options: options).ConfigureAwait(false);
+            return await SendAsync<InviteVanity>("GET", () => $"guilds/{guildId}/vanity-url", ids, options: options).ConfigureAwait(false);
         }
         public async Task<IReadOnlyCollection<InviteMetadata>> GetGuildInvitesAsync(ulong guildId, RequestOptions options = null)
         {

src/Discord.Net.Rest/Entities/Guilds/GuildHelper.cs

@@ -213,8 +213,10 @@ namespace Discord.Rest
         public static async Task<RestInviteMetadata> GetVanityInviteAsync(IGuild guild, BaseDiscordClient client,
             RequestOptions options)
         {
-            var model = await client.ApiClient.GetVanityInviteAsync(guild.Id, options).ConfigureAwait(false);
-            return RestInviteMetadata.Create(client, guild, null, model);
+            var vanityModel = await client.ApiClient.GetVanityInviteAsync(guild.Id, options).ConfigureAwait(false);
+            if (vanityModel == null) throw new InvalidOperationException("This guild does not have a vanity URL.");
+            var inviteModel = await client.ApiClient.GetInviteAsync(vanityModel.Code, options).ConfigureAwait(false);
+            return RestInviteMetadata.Create(client, guild, null, inviteModel);
         }
 
         //Roles