Don't cache empty close reasons

Commands/CloseCommand.cs

@@ -46,6 +46,8 @@ public class CloseCommand
 
         await command.RespondAsync(confirmation);
 
+        if (!string.IsNullOrWhiteSpace(reason))
+        {
             if (closeReasons.TryGetValue(command.Channel.Id, out _))
             {
                 closeReasons[command.Channel.Id] = reason;
@@ -55,6 +57,7 @@ public class CloseCommand
                 closeReasons.Add(command.Channel.Id, reason);
             }
         }
+    }
 
     public static async Task OnConfirmed(DiscordInteraction interaction)
     {