Nullable values need to be converted to null safely

[Romanx]

Not sure how this originally worked but since the changes for save access this is broken because types don't match

fixes #134

[codecov[bot]]

Codecov Report

Base: 93.13% // Head: 93.14% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (4045713) compared to base (ad7f7d8). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #136 +/- ## ======================================= Coverage 93.13% 93.14% ======================================= Files 77 77 Lines 2155 2158 +3 Branches 384 384 ======================================= + Hits 2007 2010 +3 Misses 79 79 Partials 69 69 ``` | [Impacted Files](https://codecov.io/gh/StubbleOrg/Stubble/pull/136?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=StubbleOrg) | Coverage Δ | | |---|---|---| | [...erers/TokenRenderers/InterpolationTokenRenderer.cs](https://codecov.io/gh/StubbleOrg/Stubble/pull/136/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=StubbleOrg#diff-c3JjL1N0dWJibGUuQ29tcGlsYXRpb24vUmVuZGVyZXJzL1Rva2VuUmVuZGVyZXJzL0ludGVycG9sYXRpb25Ub2tlblJlbmRlcmVyLmNz) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=StubbleOrg). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=StubbleOrg)

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