anchor.diff:  
     Map<String, StreamController<CommandEvent>> commands = {
     };
  +
  +  Function commandNotFound = (CommandEvent event) => null;
   
     String prefix;
   
  
positive.code:     }
      return true;
    }
  }
  
negative.code: 
          if (commands.containsKey(command)) {
            commands[command].add(new CommandEvent(event, command, args));
          } else {
            commandNotFound(new CommandEvent(event, command, args));
          }
        }
      });
  