Add support for `None` values in data pattern

[lundberg]

Fixes #258

[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (15522db) to head (9abede7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #259 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 22 22 Lines 2910 2910 Branches 443 444 +1 ========================================= Hits 2910 2910 ```

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