flattenObject function throws uncaught error when it recursively flat…

[skellertor]

…tens objects and a value is null. Added a check to make sure the value is not null before recursively calling the flattenObject function again.

Pull Request check-list

Please make sure to review and check all of these items:

• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
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Description of change

Added an additional check for null when flattening objects in the util.js file. Since null is a typeof object, the function would call itself and try to use the Object.keys function on null, which would then throw an error that was covering a validation error.

[SimonSchick]

Can you add a test for this?

[codecov]

Codecov Report

Merging #10293 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #10293      +/-   ##
==========================================
+ Coverage   96.27%   96.28%   +0.01%     
==========================================
  Files          68       68              
  Lines        9772     9772              
==========================================
+ Hits         9408     9409       +1     
+ Misses        364      363       -1

Impacted Files	Coverage Δ
lib/utils.js	98.62% <100%> (+0.34%)	⬆️

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[skellertor]

@SimonSchick Tests written

[sushantdhiman]

Thanks @skellertor