'JSON lookup method for S3AddPersonWidget2'

@staticmethod
def site_contact_person(r, **attr):

    site_id = r.id
    if (not site_id):
        output = current.xml.json_message(False, 400, 'No    id    provided!')
        raise HTTP(400, body=output)
    db = current.db
    s3db = current.s3db
    ltable = s3db.hrm_human_resource_site
    htable = db.hrm_human_resource
    query = (((ltable.site_id == site_id) & (ltable.site_contact == True)) & (ltable.human_resource_id == htable.id))
    person = db(query).select(htable.person_id, limitby=(0, 1)).first()
    if person:
        fake = Storage(id=person.person_id, tablename='org_site')
        return s3db.pr_person_lookup(fake, **attr)
    else:
        current.response.headers['Content-Type'] = 'application/json'
        output = json.dumps(None, separators=SEPARATORS)
        return output
