Game crashed when creating a single biome world with a custom biome / java.lang.NullPointerException: Cannot invoke "bze.a()" because the return value of "bzg.a(int, int, int)" is null

When choosing a single biome custom world the game crashed on me giving me an error message.

{{Description: Unexpected errorDescription: Unexpected error}}
java.lang.NullPointerException: Cannot invoke "bze.a()" because the return value of "bzg.a(int, int, int)" is null at ejs.a(SourceFile:587) at agr.a(SourceFile:39) at ejs.a(SourceFile:587) at enk.a(SourceFile:88) at enq.a(SourceFile:1233) at enl.a(SourceFile:1026) at enl.a(SourceFile:810) at dvx.f(SourceFile:1112) at dvx.e(SourceFile:728) at net.minecraft.client.main.Main.main(SourceFile:228) 

When copying just the stone shores biome .json and adding a custom feature it gave a different error:

Description: Unexpected error
java.lang.NullPointerException: Cannot invoke "bzm.a()" because the return value of "bzo.a(int, int, int)" is null at ekl.a(SourceFile:591) at agw.a(SourceFile:39) at ekl.a(SourceFile:591) at eod.a(SourceFile:88) at eoj.a(SourceFile:1235) at eoe.a(SourceFile:1026) at eoe.a(SourceFile:810) at dwq.f(SourceFile:1119) at dwq.e(SourceFile:735) at net.minecraft.client.main.Main.main(SourceFile:238

How to reproduce:

1. Download the provided data pack

2. Choose a single biome world using the biome "fsb:glowstone_cave"

3. The game should crash and give an error message.