Fixes #583 - Allow inserting columns for dataset with headers and no values

[codecov[bot]]

Codecov Report

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

Project coverage is 92.51%. Comparing base (4fd9a68) to head (0ce9215).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #584 +/- ## ======================================= Coverage 92.50% 92.51% ======================================= Files 28 28 Lines 2949 2952 +3 ======================================= + Hits 2728 2731 +3 Misses 221 221 ```

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