Fix #197 - None and flattening

[lmazuel]

Fix #197

[codecov-io]

Codecov Report

Merging #198 into master will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #198      +/-   ##
==========================================
- Coverage   87.64%   87.58%   -0.06%     
==========================================
  Files          25       25              
  Lines        2638     2642       +4     
==========================================
+ Hits         2312     2314       +2     
- Misses        326      328       +2     

Impacted Files	Coverage Δ
msrest/serialization.py	91.08% <100.00%> (-0.18%)	⬇️

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