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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _activity_helper(modifier: str, location=None):
 """Make an activity dictionary. :param str modifier: :param Optional[dict] location: An entity from :func:`pybel.dsl.entity` :rtype: dict """

    rv = {MODIFIER: modifier}

    if location:
        rv[LOCATION] = location

    return rv