Fix check for empty string values

[mrbean-bremen]

• broke handling of empty type 2 enumerated values
• fixes Pupil Dilated and Patient Eye Movement error when empty, even when they are allowed to be empty #147

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.65%. Comparing base (e8644e2) to head (febc6d9).
Report is 66 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
+ Coverage   89.82%   90.65%   +0.82%     
==========================================
  Files          15       15              
  Lines        1632     1722      +90     
==========================================
+ Hits         1466     1561      +95     
+ Misses        166      161       -5     

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