Include empty string values

[rongduan-zhu]

Empty query strings are included in the path but they are not signed. This change will make sure that all the query params that's not None are signed.

[codecov-io]

Codecov Report

Merging #452 into dev will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #452      +/-   ##
==========================================
- Coverage   85.85%   85.83%   -0.03%     
==========================================
  Files          56       56              
  Lines        4447     4447              
  Branches      485      485              
==========================================
- Hits         3818     3817       -1     
  Misses        475      475              
- Partials      154      155       +1

Impacted Files	Coverage Δ
azure-storage-common/azure/storage/common/_auth.py	84.37% <100%> (ø)	⬆️
...torage-blob/azure/storage/blob/_upload_chunking.py	71.42% <0%> (-0.39%)	⬇️

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[rongduan-zhu]

@zezha-msft please let me know if you like this fix or prefer to just update the docs to tell people that they should not pass in an empty string for the prefix. I personally prefer this fix as this is actively stopping users from stuffing up.

[zezha-msft]

Hi @rongduan-zhu, thanks for the PR!

Could you please rebase the branch on top of dev?