Fix Intersect on intervals with nulls

[holly-smile]

Closes #1343.

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 63.69%. Comparing base (e00c396) to head (1098529).
Report is 10 commits behind head on master.

Files	Patch %	Lines
...f/cql/engine/elm/executing/IntersectEvaluator.java	71.42%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1381      +/-   ##
============================================
+ Coverage     62.26%   63.69%   +1.43%     
+ Complexity     6951     2666    -4285     
============================================
  Files           492      492              
  Lines         27727    27738      +11     
  Branches       5506     5511       +5     
============================================
+ Hits          17265    17669     +404     
+ Misses         8198     7828     -370     
+ Partials       2264     2241      -23     

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