[MC-229966] java.lang.NullPointerException when referencing an invalid template pool in start

The bug

When a configured structure feature references a template pool that doesn't exist the data pack loads fine without any warnings, but when trying to generate terrain in that dimension the server dies

How to reproduce

Create a new world and add the data pack MC-229966.zip

Teleport to the mojira:229966 dimension

/execute in mojira:229966 run teleport ~ ~ ~

Notice that the server died and there are errors in the log, despite the data pack loading without errors

Crash report

Worker-Main-10 died
java.util.concurrent.CompletionException: z: Exception generating new chunk
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:314)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)
	at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1155)
	at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:478)
	at abg.b(SourceFile:58)
	at aqx.f(SourceFile:91)
	at aqx.a(SourceFile:131)
	at aqx.run(SourceFile:99)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1434)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:295)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1016)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1665)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1598)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Caused by: z: Exception generating new chunk
	at abe.a(SourceFile:567)
	at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
	at abe.a(SourceFile:549)
	at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1146)
	... 11 more
Caused by: java.lang.NullPointerException: Cannot invoke "cyb.a(java.util.Random)" because "â˜ƒ" is null
	at cxv.a(SourceFile:269)
	at csw$a.a(SourceFile:48)
	at csw$a.a(SourceFile:34)
	at cuc.a(SourceFile:269)
	at cro.a(SourceFile:36)
	at cmn.a(SourceFile:309)
	at cmn.a(SourceFile:292)
	at cmp.e(SourceFile:53)
	at cmp.a(SourceFile:231)
	at abe.a(SourceFile:555)
	... 14 more

java.lang.NullPointerException when referencing an invalid template pool in start_pool

The bug

How to reproduce

Crash report