fix(client-core): nullish measure values [v0.29]

[vasilev-alex]

All undefined/null measure values will now be converted to 0

[codecov]

Codecov Report

Merging #3664 (0016438) into master (3af3c84) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3664   +/-   ##
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  Coverage   59.38%   59.38%           
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  Files         125      125           
  Lines       10095    10095           
  Branches     2294     2294           
=======================================
  Hits         5995     5995           
  Misses       3814     3814           
  Partials      286      286           

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[vprus]

@vasilev-alex : Alex, could I ask what was the motivation for this breaking change? In UI, it's important to distinguish between "no data yet" and "all our business metrics are 0", and this change forces the metrics to be '0'. After that, UI has no way to distinguish between those semantically different situations. Am I missing something?