Improve sanity tests

[uzhinskiy]

Pass processing if doc[field] == null
Based on #327 (comment)

Issue #327 :

Description of changes:
Calling doc [field] .toString () for null-values was throwing an error. Added check for null-value.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (dev@1fa90d8). Click here to learn what that means.
The diff coverage is 50.00%.

@@          Coverage Diff           @@
##             dev     #361   +/-   ##
======================================
  Coverage       ?   64.11%           
  Complexity     ?      291           
======================================
  Files          ?      100           
  Lines          ?     4083           
  Branches       ?      622           
======================================
  Hits           ?     2618           
  Misses         ?     1305           
  Partials       ?      160           

Flag	Coverage Δ	Complexity Δ
Kibana-reports	77.27% <50.00%> (?)	0.00 <0.00> (?)
reports-scheduler	53.28% <ø> (?)	291.00 <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...a-reports/server/routes/utils/dataReportHelpers.ts	59.25% <50.00%> (ø)	0.00 <0.00> (?)

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[zhongnansu]

Thanks for the fix

[davidcui1225]

Thanks for the fix- could you also add a small test case for this change as well?

[zhongnansu]

No response, let's merge it in and add the test case by ourself