def _merge_set_groups(group_1, group_2):
    """
    Mergers the two set groups.
    
    Merging groups is a pre-operation of difference calculation, so copying is not required.
    
    Parameters
    ----------
    group_1 : `None`, `set` of `Any`
        The first group to merge.
    group_2 : `None`, `set` of `Any`
        The second group to merge.
    
    Returns
    -------
    merged_group : `None`, `set` of `Any`
        The merged groups.
    """
    if group_1 is None:
        return group_2
    
    if group_2 is None:
        return group_1
    
    return {*group_1, *group_2}