code: def dict_of_sets_add(dictionary, key, value):
      # type: (DictUpperBound, Any, Any) -> None
      
      set_objs = dictionary.get(key, set())
      set_objs.add(value)
      dictionary[key] = set_objs
docs: Add value to a set in a dictionary by key
  
      Args:
          dictionary (DictUpperBound): Dictionary to which to add values
          key (Any): Key within dictionary
          value (Any): Value to add to set in dictionary
  
      Returns:
          None