{'type': 'object', 'properties': {'name': {'type': 'string'}, 'start_dt': {
    'type': 'string', 'format': 'date'}, 'end_dt': {'type': 'string',
    'format': 'date'}}, 'oneOf': [{'required': ['start_dt']}, {'required':
    ['end_dt']}]}
How to make json-schema to allow one but not another field?