Blob 输出绑定不支持收集器，请参阅此 问题.

Collectors are not supported for Blob output bindings, see this issue.

对于可变数量的输出 blob(在您的情况下为 0 或 1，但可以是任意数量)，您必须使用命令式绑定.从您的 function.json 中删除 collection 绑定，然后执行以下操作:

For variable amount of output blobs (0 or 1 in your case, but can be any), you would have to use imperative bindings. Remove collection binding from your function.json and then do this:

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, Binder binder)
{
    if (req.Method == HttpMethod.Post) 
    {
        string jsonContent = await req.Content.ReadAsStringAsync();

        var attributes = new Attribute[]
        {    
            new BlobAttribute("testdata/{rand-guid}.txt"),
            new StorageAccountAttribute("test_STORAGE")
        };

        using (var writer = await binder.BindAsync<TextWriter>(attributes))
        {
            writer.Write(jsonContent);
        }

        return req.CreateResponse(HttpStatusCode.OK);
    }
    else 
    {
        return req.CreateResponse(HttpStatusCode.BadRequest);    
    }
}