When create a snapshot by use CinderVolumeSnapshot class and set description,it will causea error

org.openstack4j.api.exceptions.ClientResponseException: Invalid input for field/attribute snapshot. Value: {u'display_name': u'aP2Uk2', u'name': u'aP2Uk2', u'description': u'aP2Uk2', u'display_description': u'aP2Uk2', u'volume_id': u'7adb3a1b-85e3-4dc8-b765-7d76ed79d711', u'metadata': {u'display_description': u'aP2Uk2'}}. Additional properties are not allowed (u'display_description' was unexpected)
at org.openstack4j.api.exceptions.ResponseException.mapException(ResponseException.java:58) ~[openstack4j-3.9.jar:?]
at org.openstack4j.api.exceptions.ResponseException.mapException(ResponseException.java:70) ~[openstack4j-3.9.jar:?]
at org.openstack4j.core.transport.HttpEntityHandler.handleLessThan500(HttpEntityHandler.java:99) ~[openstack4j-3.9.jar:?]
at org.openstack4j.core.transport.HttpEntityHandler.handle(HttpEntityHandler.java:45) ~[openstack4j-3.9.jar:?]
at org.openstack4j.connectors.resteasy.HttpResponseImpl.getEntity(HttpResponseImpl.java:63) ~[openstack4j-resteasy-3.9.jar:?]
at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:248) ~[openstack4j-3.9.jar:?]
at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:238) ~[openstack4j-3.9.jar:?]
at org.openstack4j.openstack.storage.block.internal.BlockVolumeSnapshotServiceImpl.create(BlockVolumeSnapshotServiceImpl.java:78) ~[openstack4j-3.9.jar:?]

In Cinder train project's source code-cinder/api/schemas/snapshots.py,it difine create snapshot parameter schema:
create = {
'type': 'object',
'properties': {
'type': 'object',
'snapshot': {
'type': 'object',
'properties': {
'name': parameter_types.name_allow_zero_min_length,
'display_name': parameter_types.name_allow_zero_min_length,
'description': parameter_types.description,
'volume_id': parameter_types.uuid_allow_null,
'force': parameter_types.boolean,
'metadata': parameter_types.metadata_allows_null,
},
'required': ['volume_id'],
'additionalProperties': False,
},
},
'required': ['snapshot'],
'additionalProperties': False,
}
I want to know why set 'display_description' in CinderVolumeSnapshot ,thank you.