Null handling by ProperContains, ProperIncludedIn, ProperIncludes, ProperIn evaluators.

[antvaset]

This fixes how the ProperContains, ProperIncludedIn, ProperIncludes, ProperIn evaluators handle nulls. The CQL specification states that:

• The T properly included in List<T> expression (ProperIn(T, List<T>) in ELM) evaluates to null if either argument is null (link).
• Same for List<T> properly included in List<T> (ProperIncludedIn(List<T>, List<T>) in ELM).
• List<T> properly includes T (ProperContains(List<T>, T) in ELM) evaluates to null if either argument is null (link).
• Same for List<T> properly includes List<T> (ProperIncludes(List<T>, List<T>) in ELM).

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 62.25%. Comparing base (e00c396) to head (0f022ba).
Report is 2 commits behind head on master.

Files	Patch %	Lines
.../engine/elm/executing/ProperContainsEvaluator.java	50.00%	0 Missing and 1 partial ⚠️
...qf/cql/engine/elm/executing/ProperInEvaluator.java	50.00%	0 Missing and 1 partial ⚠️
.../engine/elm/executing/ProperIncludesEvaluator.java	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1370      +/-   ##
============================================
- Coverage     62.26%   62.25%   -0.01%     
+ Complexity     6951     6945       -6     
============================================
  Files           492      492              
  Lines         27727    27713      -14     
  Branches       5506     5502       -4     
============================================
- Hits          17265    17254      -11     
  Misses         8198     8198              
+ Partials       2264     2261       -3     

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[JPercival]

@antvaset - We have a goal of >=80% test coverage for new/updated code. Can you add tests for the Evaluators that gets the patch up to 80%?