[FIX] Heatmap: Split by missing values

[ales-erjavec]

Issue

Fixes gh-4684

Description of changes

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4686 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4686      +/-   ##
==========================================
- Coverage   83.70%   83.69%   -0.02%     
==========================================
  Files         280      275       -5     
  Lines       56436    55644     -792     
==========================================
- Hits        47241    46571     -670     
+ Misses       9195     9073     -122     

[Hrovatin]

This does not crash anymore. However, it is not what I expected from splitting with missing values: The missing values should be grouped in a separate N/A group (as in colour annotation legend). The behavior that was implemented by this fix can be already achieved by using Select Rows -> is defined.

[Hrovatin]

Now it works as expected.

[ajdapretnar]

This works well for me.