Made changes per discussion

src/Discord.Net.Core/RequestOptions.cs

@@ -5,7 +5,6 @@ namespace Discord
     public class RequestOptions
     {
         public static RequestOptions Default => new RequestOptions();
-        public static RequestOptions WithReason(string reason) => new RequestOptions { AuditLogReason = reason };
 
         /// <summary> 
         /// The max time, in milliseconds, to wait for this request to complete. If null, a request will not time out. 

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -803,7 +803,8 @@ namespace Discord.API
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
-            await SendAsync("PUT", () => $"guilds/{guildId}/bans/{userId}?delete-message-days={args.DeleteMessageDays}&reason={args.Reason}", ids, options: options).ConfigureAwait(false);
+            string reason = string.IsNullOrWhiteSpace(args.Reason) ? "" : $"&reason={args.Reason}";
+            await SendAsync("PUT", () => $"guilds/{guildId}/bans/{userId}?delete-message-days={args.DeleteMessageDays}{reason}", ids, options: options).ConfigureAwait(false);
         }
         public async Task RemoveGuildBanAsync(ulong guildId, ulong userId, RequestOptions options = null)
         {
@@ -987,7 +988,8 @@ namespace Discord.API
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
-            await SendAsync("DELETE", () => $"guilds/{guildId}/members/{userId}?reason={reason}", ids, options: options).ConfigureAwait(false);
+            reason = string.IsNullOrWhiteSpace(reason) ? "" : $"?reason={reason}";
+            await SendAsync("DELETE", () => $"guilds/{guildId}/members/{userId}{reason}", ids, options: options).ConfigureAwait(false);
         }
         public async Task ModifyGuildMemberAsync(ulong guildId, ulong userId, Rest.ModifyGuildMemberParams args, RequestOptions options = null)
         {

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

@@ -107,9 +107,9 @@ namespace Discord.Rest
         }
 
         public static async Task AddBanAsync(IGuild guild, BaseDiscordClient client,
-            ulong userId, int pruneDays, RequestOptions options)
+            ulong userId, int pruneDays, string reason, RequestOptions options)
         {
-            var args = new CreateGuildBanParams { DeleteMessageDays = pruneDays };
+            var args = new CreateGuildBanParams { DeleteMessageDays = pruneDays, Reason = reason };
             await client.ApiClient.CreateGuildBanAsync(guild.Id, userId, args, options).ConfigureAwait(false);
         }
         public static async Task RemoveBanAsync(IGuild guild, BaseDiscordClient client,

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

@@ -138,9 +138,9 @@ namespace Discord.Rest
             => GuildHelper.GetBansAsync(this, Discord, options);
 
         public Task AddBanAsync(IUser user, int pruneDays = 0, string reason = null, RequestOptions options = null)
-            => GuildHelper.AddBanAsync(this, Discord, user.Id, pruneDays, options);
+            => GuildHelper.AddBanAsync(this, Discord, user.Id, pruneDays, reason, options);
         public Task AddBanAsync(ulong userId, int pruneDays = 0, string reason = null, RequestOptions options = null)
-            => GuildHelper.AddBanAsync(this, Discord, userId, pruneDays, options);
+            => GuildHelper.AddBanAsync(this, Discord, userId, pruneDays, reason, options);
 
         public Task RemoveBanAsync(IUser user, RequestOptions options = null)
             => GuildHelper.RemoveBanAsync(this, Discord, user.Id, options);

src/Discord.Net.Rest/Net/DefaultRestClient.cs

@@ -67,7 +67,7 @@ namespace Discord.Net.Rest
             string uri = Path.Combine(_baseUrl, endpoint);
             using (var restRequest = new HttpRequestMessage(GetMethod(method), uri))
             {
-                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", reason);
+                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", Uri.EscapeDataString(reason));
                 return await SendInternalAsync(restRequest, cancelToken, headerOnly).ConfigureAwait(false);
             }
         }
@@ -76,7 +76,7 @@ namespace Discord.Net.Rest
             string uri = Path.Combine(_baseUrl, endpoint);
             using (var restRequest = new HttpRequestMessage(GetMethod(method), uri))
             {
-                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", reason);
+                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", Uri.EscapeDataString(reason));
                 restRequest.Content = new StringContent(json, Encoding.UTF8, "application/json");
                 return await SendInternalAsync(restRequest, cancelToken, headerOnly).ConfigureAwait(false);
             }
@@ -86,7 +86,7 @@ namespace Discord.Net.Rest
             string uri = Path.Combine(_baseUrl, endpoint);
             using (var restRequest = new HttpRequestMessage(GetMethod(method), uri))
             {
-                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", reason);
+                if (reason != null) restRequest.Headers.Add("X-Audit-Log-Reason", Uri.EscapeDataString(reason));
                 var content = new MultipartFormDataContent("Upload----" + DateTime.Now.ToString(CultureInfo.InvariantCulture));
                 if (multipartParams != null)
                 {

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -282,9 +282,9 @@ namespace Discord.WebSocket
             => GuildHelper.GetBansAsync(this, Discord, options);
 
         public Task AddBanAsync(IUser user, int pruneDays = 0, string reason = null, RequestOptions options = null)
-            => GuildHelper.AddBanAsync(this, Discord, user.Id, pruneDays, options);
+            => GuildHelper.AddBanAsync(this, Discord, user.Id, pruneDays, reason, options);
         public Task AddBanAsync(ulong userId, int pruneDays = 0, string reason = null, RequestOptions options = null)
-            => GuildHelper.AddBanAsync(this, Discord, userId, pruneDays, options);
+            => GuildHelper.AddBanAsync(this, Discord, userId, pruneDays, reason, options);
 
         public Task RemoveBanAsync(IUser user, RequestOptions options = null)
             => GuildHelper.RemoveBanAsync(this, Discord, user.Id, options);