Release build failing with `minifyRelease` enabled citing an unexpected usage left in retrosheet

I tried created a release today with minifyRelease enabled and was presented with this error:

```
"com.android.tools.r8.internal.GG: Unexpected usage left in method 
boolean com.github.theapache64.retrosheet.utils.JsonValidator.isValidJsonObject(java.lang.String)
after inlining: Bg  v65 <- v3; com.squareup.moshi.JsonAdapter$2"
```

Here's my project: https://github.com/racka98/ThinkRchive