<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def dict_of_sets_add(dictionary, key, value):
 # type: (DictUpperBound, Any, Any) -> None """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 """

    set_objs = dictionary.get(key, set())
    set_objs.add(value)
    dictionary[key] = set_objs