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': 'INTERNAL', 'name_': 'Q2277', 'id': 1, 'label': 'Roman Empire'}, {'type': 'INTERNAL', 'name_': 'Q39018', 'id': 2, 'label': 'emperor'}, {'type': 'INTERNAL', 'name_': 'Q235090', 'id': 3, 'label': 'Julia Avita Mamaea'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q1446', 'id': 4, 'label': 'Caracalla'}, {'type': 'INTERNAL', 'name_': 'Q312584', 'id': 5, 'label': 'Constitutio Antoniniana'}], 'links': [{'name_': 'P361', 'source': 0, 'target': 1, 'label': 'part of'}, {'name_': 'P279', 'source': 0, 'target': 2, 'label': 'subclass of'}, {'name_': 'P1906', 'source': 1, 'target': 0, 'label': 'office held by head of state'}, {'name_': 'P39', 'source': 3, 'target': 2, 'label': 'position held'}, {'name_': 'P451', 'source': 3, 'target': 4, 'label': 'unmarried partner'}, {'name_': 'P1001', 'source': 5, 'target': 1, 'label': 'applies to jurisdiction'}, {'name_': 'P138', 'source': 5, 'target': 4, 'label': 'named after'}]}