[FIX] Fix impute.Model for derived domains

[markotoplak]

Issue

Found at #6644, but per @VesnaT's comment does not fix it because another check fails.
Fixes #6644 (after @VesnaT's commit).

Description of changes

The compute_value was missing transformation into the variable space it was working upon.

Thanks to @VesnaT for providing minimum code that reproduced the error.

Includes

• Code changes
• Tests
• Documentation

[VesnaT]

The fix does not prevent the Prediction error message, it only changes it.

[markotoplak]

@VesnaT, thanks. I removed the "fixes" statement in the issue description, but think that this is still a step forward and that this PR should be merged.

[codecov]

Codecov Report

Merging #6668 (3752aea) into master (e5ceec7) will decrease coverage by 0.01%.
Report is 10 commits behind head on master.
The diff coverage is 88.88%.

❗ Current head 3752aea differs from pull request most recent head 0547537. Consider uploading reports for the commit 0547537 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6668      +/-   ##
==========================================
- Coverage   88.10%   88.10%   -0.01%     
==========================================
  Files         321      321              
  Lines       69946    69950       +4     
==========================================
+ Hits        61628    61629       +1     
- Misses       8318     8321       +3