Cannot handle properly when bedrock response with empty string

[Shellmode]

Describe the bug
当 bedrock 返回空字符串的时候，在 https://github.com/aws-samples/bedrock-access-gateway/blob/main/src/api/models/bedrock.py#L456 处会报错，trace 如下

Please complete the following information:

• Which API you used: [e.g. /chat/completions]
• [] Which model you used: [e.g. anthropic.claude-3-sonnet-20240229-v1:0]

To Reproduce
Steps to reproduce the behavior. If possible, please share an example request.

curl http://Bedroc-Proxy-abcdefg-123123.us-west-2.elb.amazonaws.com/api/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer bedrock" \
  -d '{
    "model": "anthropic.claude-3-5-sonnet-20240620-v1:0",
    "messages": [
      {"role": "user", "content": "Given a [text fragment], extract the person names from it. Note that: 1. List the person names directly, separated by commas, like this: Mary, Mike, Lucy. 2. If no characters are recognized in the [text fragment], return an empty string directly, without adding any explanations or comments. 3. Do not output any additional text or explanations. Text fragment: \"Darkness.\"He suddenly woke up, and that was his first thought.\" Extracting result:"}
    ]
  }'

Expected behavior
Response with empty string

Screenshots

Additional context
Add any other context about the problem here.

[daixba]

我测试了下， 是因为 bedrock 返回content 为空， 如下所示：
'message': {'role': 'assistant', 'content': []}}, 'stopReason': 'end_turn',

针对这种情况就返回为空：

{"id":"chatcmpl-a3aa1356","created":1723196261,"model":"anthropic.claude-3-5-sonnet-20240620-v1:0","system_fingerprint":"fp","choices":[{"index":0,"finish_reason":"stop","logprobs":null,"message":{"role":"assistant"}}],"object":"chat.completion","usage":{"prompt_tokens":112,"completion_tokens":4,"total_tokens":116}}

fix 代码见： 2950c15

[daixba]

参考 https://github.com/aws-samples/bedrock-access-gateway/blob/main/README_CN.md#%E5%A6%82%E4%BD%95%E5%8D%87%E7%BA%A7 进行更新

要使用最新功能,您无需重新部署CloudFormation堆栈。您只需拉取最新的镜像即可。

具体操作方式取决于您部署的版本:

Lambda版本: 进入AWS Lambda控制台,找到Lambda 函数，然后找到并单击部署新映像按钮,然后单击保存。
Fargate版本: 进入ECS控制台,单击ECS集群,转到任务选项卡,选择正在运行的唯一任务,然后点击停止所选菜单, ECS会自动启动新任务并且使用最新镜像。