TransactionWrite sanitizes items

[ckhsponge]

TransactionWrite should call sanitize_item so that nils are not persisted. Otherwise GSI will fail with a nil range key.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.88%. Comparing base (37572d7) to head (20d2eea). Report is 27 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #897      +/-   ##
==========================================
+ Coverage   91.56%   91.88%   +0.31%     
==========================================
  Files          75       76       +1     
  Lines        3700     3856     +156     
==========================================
+ Hits         3388     3543     +155     
- Misses        312      313       +1     

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[ckhsponge]

This was bothering me again today. I'll renew my efforts to fix it.

[ckhsponge]

@andrykonchin A review of this would be appreciated. Let me know if you see some areas for cleanup.

[andrykonchin]

I'll review this later this week.

[ckhsponge]

@andrykonchin Please review again.