769 refine empty nonempty operators logic

[koalyptus]

Description

Addresses issue #769

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes do not lower current test coverage
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

Merging #784 into master will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #784   +/-   ##
=======================================
  Coverage   89.09%   89.09%           
=======================================
  Files          39       39           
  Lines        4504     4504           
  Branches      327      327           
=======================================
  Hits         4013     4013           
  Misses        475      475           
  Partials       16       16           

Impacted Files	Coverage Δ
src/tablefilter.js	93.48% <100.00%> (ø)

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