If you only expect one name, why do you accept varargrs? `super` (`Enumerable`'s `group_by`) doesn't accept args at all (other than block), so there is no need to pass them up.

Granted, it might be interesting for multi-arg `group_by` to work, returning nested structure such as:

```ruby
array.group_by(:first_attr, :second_attr)
  
# =>
#  
#   { 
#    :first_value_1 => { :second_value_1 => array[0], :second_value_2 => array[1] }, 
#    :first_value_2 =>  { :second_value_1 => array[2], :second_value_2 => array[3] }
#  } 
```