在代码中添加异常处理来确保在调用PutLogEvents API时有可用的nextSequenceToken参数。以下是Python的示例代码：

import boto3
import time

client = boto3.client('logs')

log_group_name = 'example-log-group'
log_stream_name = 'example-log-stream'

# try to get the next sequence token for the log stream
try:
    response = client.describe_log_streams(logGroupName=log_group_name, logStreamNamePrefix=log_stream_name)
    next_sequence_token = response['logStreams'][0]['uploadSequenceToken']
except Exception as e:
    next_sequence_token = None

# log some messages
log_events = [
    {
        'timestamp': int(time.time() * 1000),
        'message': 'example log message'
    }
]

# if there is a next sequence token, use it as a parameter for the PutLogEvents API
if next_sequence_token:
    response = client.put_log_events(
        logGroupName=log_group_name,
        logStreamName=log_stream_name,
        logEvents=log_events,
        sequenceToken=next_sequence_token
    )
else:
    response = client.put_log_events(
        logGroupName=log_group_name,
        logStreamName=log_stream_name,
        logEvents=log_events
    )

print(response)