Via https://github.com/spring-projects/spring-boot/issues/21431 and somewhat similar to https://github.com/spring-projects/spring-framework/issues/25050, it appears that ResolvableType needs to handle a TypeNotPresentException being thrown when it queries generics. Here's the failure from the Boot issue:

java.lang.TypeNotPresentException: Type org.springframework.jdbc.CannotGetJdbcConnectionException not present
    at java.base/sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:117)
    at java.base/sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:125)
    at java.base/sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
    at java.base/sun.reflect.generics.visitor.Reifier.reifyTypeArguments(Reifier.java:68)
    at java.base/sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:138)
    at java.base/sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
    at java.base/sun.reflect.generics.repository.ClassRepository.computeSuperclass(ClassRepository.java:104)
    at java.base/sun.reflect.generics.repository.ClassRepository.getSuperclass(ClassRepository.java:86)
    at java.base/java.lang.Class.getGenericSuperclass(Class.java:955)
    at org.springframework.core.ResolvableType.getSuperType(ResolvableType.java:467)
    at org.springframework.core.ResolvableType.as(ResolvableType.java:456)
    at org.springframework.core.ResolvableType.forClass(ResolvableType.java:1041)
    at org.springframework.boot.diagnostics.AbstractFailureAnalyzer.getCauseType(AbstractFailureAnalyzer.java:56)
    at org.springframework.boot.diagnostics.AbstractFailureAnalyzer.analyze(AbstractFailureAnalyzer.java:33)
    at org.springframework.boot.diagnostics.FailureAnalyzers.analyze(FailureAnalyzers.java:111)
    at org.springframework.boot.diagnostics.FailureAnalyzers.reportException(FailureAnalyzers.java:104)
    at org.springframework.boot.SpringApplication.reportFailure(SpringApplication.java:816)
    at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:801)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:325)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
    at at.mikemitterer.catshostel.Application$Companion.main(Application.kt:46)
    at at.mikemitterer.catshostel.Application.main(Application.kt)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: java.lang.ClassNotFoundException: org.springframework.jdbc.CannotGetJdbcConnectionException
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
    at java.base/java.lang.Class.forName0(Native Method)
    at java.base/java.lang.Class.forName(Class.java:416)
    at java.base/sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:114)
    ... 27 common frames omitted