Which Roman Emperor led from 198 to 217 but never had children?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'QUESTIONS_ENTITY', 'name_': 'Q842606', 'id': 0, 'label': 'Roman emperor'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q6992597', 'id': 1, 'label': 'Category:Roman emperors'}], 'links': [{'name_': 'P910', 'source': 0, 'target': 1, 'label': "topic's main category"}]}