Empty string in CloudBlockBlob metadata causes CPU leak.

[ansario]

The Azure Storage Rest API allows PUTing empty string values in the metadata of a CloudBlockBlob by setting the optional request header x-ms-meta-name to "". The C# nuget package (8.7.0) does not return when calling the .ListBlobs() method on a CloudBlobDirectory when one of the CloudBlockBlobs in the directory has a few, but not all, metadata values set to empty string. On each subsequent request, CPU increases by about 10%.

Steps to reproduce:

1. Create CloudBlockBlob with several metadata Keys + non empty string values via the REST API.
2. Add one additional metadata key with an empty string value via the REST API.
3. Using C# 8.7.0 nuget package, call .ListBlobs() on parent CloudBlobDirectory of the CloudBlockBlob.
4. Observe CPU spike and infinte hang.

[kfarmer-msft]

@ansario Does this still repro for you under 9.3.2 or 9.4.0? In particular, are you using sync or async APIs when you repro?

[seanmcc-msft]

Duplicate of #828