[ENH] Add no empty option

[arnaudbore]

Quick description

Close #1282

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Type of change

Check the relevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

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Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.59%. Comparing base (eaf3b4b) to head (02b6556).
⚠️ Report is 2 commits behind head on master.

❌ Your project status has failed because the head coverage (72.59%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1283      +/-   ##
==========================================
- Coverage   72.60%   72.59%   -0.01%     
==========================================
  Files         294      294              
  Lines       25338    25339       +1     
  Branches     3546     3546              
==========================================
- Hits        18396    18395       -1     
  Misses       5447     5447              
- Partials     1495     1497       +2     

Flag	Coverage Δ
smoketests	69.78% <100.00%> (+<0.01%)	⬆️
unittests	13.28% <0.00%> (-0.01%)	⬇️

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Components	Coverage Δ
Scripts	75.44% <100.00%> (+<0.01%)	⬆️
Library	69.19% <ø> (-0.02%)	⬇️

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