Return Exception instead of plain error string

[ci skip]

nyxx/lib/src/Nyxx.dart

@@ -304,7 +304,7 @@ class Nyxx implements Disposable {
   /// ```
   Future<Guild> createGuild(GuildBuilder builder) async {
     if (this.guilds.count >= 10) {
-      return Future.error("Guild cannot be created if bot is in 10 or more guilds");
+      return Future.error(ArgumentError("Guild cannot be created if bot is in 10 or more guilds"));
     }
 
     final response = await this._http._execute(BasicRequest._new("/guilds", method: "POST"));

nyxx/lib/src/core/channel/MessageChannel.dart

@@ -120,7 +120,7 @@ abstract class MessageChannel implements Channel, ISend, Disposable {
     if (files != null && files.isNotEmpty) {
       for (final file in files) {
         if (file._bytes.length > fileUploadLimit) {
-          return Future.error("File with name: [${file._name}] is too big!");
+          return Future.error(ArgumentError("File with name: [${file._name}] is too big!"));
         }
       }
 

nyxx/lib/src/core/channel/guild/GuildChannel.dart

@@ -114,7 +114,7 @@ abstract class CachelessGuildChannel extends IGuildChannel {
   @override
   Future<void> editChannelPermissions(PermissionsBuilder perms, SnowflakeEntity entity, {String? auditReason}) async {
     if (entity is! IRole && entity is! User) {
-      return Future.error(Exception("The `id` property must be either Role or User"));
+      return Future.error(ArgumentError("The `id` property must be either Role or User"));
     }
 
     final permSet = perms._build();

nyxx/lib/src/core/channel/guild/TextChannel.dart

@@ -61,7 +61,7 @@ abstract class GuildTextChannel implements Channel, CachelessGuildChannel, IText
   /// ```
   Future<Webhook> createWebhook(String name, {File? avatarFile, String? auditReason}) async {
     if (name.isEmpty || name.length > 80) {
-      return Future.error("Webhook name cannot be shorter than 1 character and longer than 80 characters");
+      return Future.error(ArgumentError("Webhook name cannot be shorter than 1 character and longer than 80 characters"));
     }
 
     final body = <String, dynamic>{"name": name};

nyxx/lib/src/core/guild/Guild.dart

@@ -303,11 +303,11 @@ class Guild extends SnowflakeEntity implements Disposable {
   /// ```
   Future<GuildEmoji> createEmoji(String name, {List<Role>? roles, File? image, List<int>? imageBytes}) async {
     if (image != null && await image.length() > 256000) {
-      return Future.error("Emojis and animated emojis have a maximum file size of 256kb.");
+      return Future.error(ArgumentError("Emojis and animated emojis have a maximum file size of 256kb."));
     }
 
     if (image == null && imageBytes == null) {
-      return Future.error("Both imageData and file fields cannot be null");
+      return Future.error(ArgumentError("Both imageData and file fields cannot be null"));
     }
 
     final body = <String, dynamic>{
@@ -408,7 +408,7 @@ class Guild extends SnowflakeEntity implements Disposable {
     final channel = this.channels.first as CacheGuildChannel?;
 
     if (channel == null) {
-      return Future.error("Cannot get any channel to create invite to");
+      return Future.error(ArgumentError("Cannot get any channel to create invite to"));
     }
 
     return channel.createInvite(
@@ -535,11 +535,11 @@ class Guild extends SnowflakeEntity implements Disposable {
       String? auditReason}) async {
     // Checks to avoid API panic
     if (type == ChannelType.dm || type == ChannelType.groupDm) {
-      return Future.error("Cannot create DM channel.");
+      return Future.error(ArgumentError("Cannot create DM channel."));
     }
 
     if (type == ChannelType.category && parent != null) {
-      return Future.error("Cannot create Category Channel which have parent channel.");
+      return Future.error(ArgumentError("Cannot create Category Channel which have parent channel."));
     }
 
     // Construct body
@@ -580,7 +580,7 @@ class Guild extends SnowflakeEntity implements Disposable {
     } else if (absolute != null) {
       newPosition = absolute;
     } else {
-      return Future.error("Cannot move channel by zero places");
+      return Future.error(ArgumentError("Cannot move channel by zero places"));
     }
 
     await client._http._execute(BasicRequest._new("/guilds/${this.id}/channels",

nyxx/lib/src/core/message/GuildEmoji.dart

@@ -80,7 +80,7 @@ class GuildEmoji extends IGuildEmoji implements SnowflakeEntity, GuildEntity {
   /// Allows to edit emoji
   Future<GuildEmoji> edit({String? name, List<Snowflake>? roles}) async {
     if (name == null && roles == null) {
-      return Future.error("Both name and roles fields cannot be null");
+      return Future.error(ArgumentError("Both name and roles fields cannot be null"));
     }
 
     final body = <String, dynamic>{

nyxx/lib/src/core/message/Message.dart

@@ -230,7 +230,7 @@ abstract class Message extends SnowflakeEntity implements Disposable {
   /// Edits the message.
   Future<Message> edit({dynamic content, EmbedBuilder? embed, AllowedMentions? allowedMentions}) async {
     if (this.author.id != client.self.id) {
-      return Future.error("Cannot edit someones message");
+      return Future.error(ArgumentError("Cannot edit someones message"));
     }
 
     final body = <String, dynamic>{