Error loading registry data: Missing value [0] : ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:fossil]

When adding my worldgen data pack to the game, the game fails to validate it because of this error: java.util.concurrent.CompletionException: com.google.gson.JsonParseException: Error loading registry data: Missing value [0] : ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:fossil]

As far as I know, fossils don't have a configured structure feature file. So I do not know how to fix this as it is a Minecraft worldgen error and I have not done anything to affect Minecraft's worldgen.
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How to reproduce:*

1. Download provided data pack

2. Add it to a new world

3. Notice that the debug log gives an error about fossils.