fix(eslint-plugin): [nuta] correctly handle null/undefined separation

[bradzacher]

Fixes #1199

[typescript-eslint]

Thanks for the PR, @bradzacher!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #1201 into master will increase coverage by <.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #1201      +/-   ##
==========================================
+ Coverage   94.15%   94.15%   +<.01%     
==========================================
  Files         124      124              
  Lines        5336     5339       +3     
  Branches     1492     1493       +1     
==========================================
+ Hits         5024     5027       +3     
  Misses        178      178              
  Partials      134      134

Impacted Files	Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts	88.6% <80%> (+0.44%)	⬆️