backport: Fix corner cases of combine_selection. (#1038)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.35%. Comparing base (4a326f3) to head (5d968bd). Report is 1 commits behind head on v2.x.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## v2.x #1040 +/- ## ========================================== + Coverage 86.24% 86.35% +0.11% ========================================== Files 90 90 Lines 5902 5952 +50 ========================================== + Hits 5090 5140 +50 Misses 812 812 ```

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