list_blobs() crashes due to response from blob storage not containing Creation-Time

Which service(blob, file, queue) does this issue concern?

blob

Which version of the SDK was used? Please provide the output of pip freeze.

azure-storage-blob==2.1.0
azure-storage-common==2.1.0
azure-common==1.1.23

What problem was encountered?

Call to list_blobs(container_name) throws an error in the end when the blobs have been created by the client on an IoTEdgeBlobStorage. The issue is that the Creation-Time appears to be empty when the request returns from the IoTEdge module. eg:
`

     <Name>test.txt</Name>
     <Properties>
        <Creation-Time />
        <Last-Modified>Tue, 20 Aug 2019 08:12:37 GMT</Last-Modified>
        <Etag>0x8D7254629E53C01</Etag>
        <Content-Length>32</Content-Length>
        <Content-Type>application/octet-stream</Content-Type>
        <Content-Encoding />
        <Content-Language />
        <Content-MD5>DdOF7ew/k5qHSdf00h0hzg==</Content-MD5>
        <Cache-Control />
        <Content-Disposition />
        <BlobType>BlockBlob</BlobType>
        <LeaseStatus>unlocked</LeaseStatus>
        <LeaseState>available</LeaseState>
        <ServerEncrypted>false</ServerEncrypted>
     </Properties>
  </Blob>`

If you look at azure/storage/blob/_deserialization.py on you see something like setattr(blob.properties, info[1], info[2](property_element.text))

if the Creation-Time is empty this property_element.text is None which makes the call to the info[2] (parser.parse) crash

Have you found a mitigation/solution?

Yes and no. You could test to see if property_element.text is empty or not. But I don't know if this is the way to go. It's maybe better to make sure that the blob storage returns a Creation-Time property.

从 azure/storage/blob/_deserialization.py 开始，跟踪围绕 Creation-Time 属性的 list_blobs 响应解析过程。使用 Creation-Time 为空的 Blob 响应重现该故障，然后确定预期的处理方式，并验证 list_blobs 能够完成且不会导致解析器崩溃。