Fix getindex on solution object with averages

[codecov[bot]]

Codecov Report

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

Comparison is base (daeee90) 78.91% compared to head (9f3bf40) 78.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #190 +/- ## ========================================== + Coverage 78.91% 78.96% +0.05% ========================================== Files 26 26 Lines 5254 5254 ========================================== + Hits 4146 4149 +3 + Misses 1108 1105 -3 ```

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