Change grouping type int -> string

src/Discord.Net.Commands/Attributes/PreconditionAttribute.cs

@@ -8,10 +8,10 @@ namespace Discord.Commands
     {
         /// <summary>
         /// Specify a group that this precondition belongs to. Preconditions of the same group require only one
-        /// of the preconditions to pass in order to be successful (A || B). Specifying <see cref="Group"/> = 0
+        /// of the preconditions to pass in order to be successful (A || B). Specifying <see cref="Group"/> = <see cref="null"/>
         /// or not at all will require *all* preconditions to pass, just like normal (A &amp;&amp; B).
         /// </summary>
-        public int Group { get; set; } = 0;
+        public string Group { get; set; } = null;
 
         public abstract Task<PreconditionResult> CheckPermissions(ICommandContext context, CommandInfo command, IServiceProvider services);
     }

src/Discord.Net.Commands/Info/CommandInfo.cs

@@ -70,9 +70,9 @@ namespace Discord.Commands
 
             async Task<PreconditionGroupResult> CheckGroups(IEnumerable<PreconditionAttribute> preconditions, string type)
             {
-                foreach (IGrouping<int, PreconditionAttribute> preconditionGroup in preconditions.GroupBy(p => p.Group))
+                foreach (IGrouping<string, PreconditionAttribute> preconditionGroup in preconditions.GroupBy(p => p.Group))
                 {
-                    if (preconditionGroup.Key == 0)
+                    if (preconditionGroup.Key == null)
                     {
                         foreach (PreconditionAttribute precondition in preconditionGroup)
                         {