Refine support for custom application class

[hdeadman]

I am working on trying to build an application where the class containing @SpringBootApplication comes from a dependency. It would be nice if we could optionally specify the name of the main class as an alternative to it being searched for. The current error I am running into is a NullPointerException when QuartzHints is processing, due to it not being able to determine the package of the main class.

./gradlew build

> Task :generateAot
2021-11-06 21:41:04.631  WARN 2560 --- [           main] o.s.a.build.ContextBootstrapContributor  : No application class detected, skipping context bootstrap generation
2021-11-06 21:41:05.905  INFO 2560 --- [           main] o.s.nativex.support.SpringAnalyzer       : Spring Native operating mode: native

> Task :compileAotMainJava
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: /home/hdeadman/git/cas-overlay-template/build/generated/sources/aotMain/org/springframework/aot/StaticSpringFactories.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :generateTestAot
WARNING: Unable to find jar '/home/hdeadman/git/cas-overlay-template/build/classes/java/test' whilst scanning filesystem
WARNING: Unable to find jar '/home/hdeadman/git/cas-overlay-template/build/resources/test' whilst scanning filesystem
2021-11-06 21:41:36.485  INFO 2611 --- [           main] o.s.nativex.support.SpringAnalyzer       : Spring Native operating mode: native
java.lang.NullPointerException
        at java.base/java.lang.String.contains(String.java:2036)
        at org.springframework.nativex.type.TypeSystem.findDirectoriesOrTargetDirJar(TypeSystem.java:1355)
        at org.springframework.nativex.type.TypeSystem.scan(TypeSystem.java:1512)
        at org.springframework.nativex.type.Type.getSubtypes(Type.java:3081)
        at org.springframework.scheduling.quartz.QuartzHints.computeHints(QuartzHints.java:115)
        at org.springframework.nativex.type.SpringConfiguration.<init>(SpringConfiguration.java:58)
        at org.springframework.nativex.type.TypeSystem.ensureSpringConfigurationDiscovered(TypeSystem.java:914)
        at org.springframework.nativex.type.TypeSystem.getAccessCheckers(TypeSystem.java:1305)
        at org.springframework.nativex.support.ReflectionHandler.addAccess(ReflectionHandler.java:142)
        at org.springframework.nativex.support.ReflectionHandler.addAccess(ReflectionHandler.java:91)
        at org.springframework.nativex.support.ReflectionHandler.registerWebApplicationTypeClasses(ReflectionHandler.java:65)
        at org.springframework.nativex.support.ReflectionHandler.register(ReflectionHandler.java:71)
        at org.springframework.nativex.support.SpringAnalyzer.analyze(SpringAnalyzer.java:86)
        at org.springframework.aot.nativex.ConfigurationContributor.contribute(ConfigurationContributor.java:71)
        at org.springframework.aot.build.BootstrapCodeGenerator.generate(BootstrapCodeGenerator.java:90)
        at org.springframework.aot.build.BootstrapCodeGenerator.generate(BootstrapCodeGenerator.java:68)
        at org.springframework.aot.test.build.GenerateTestBootstrapCommand.call(GenerateTestBootstrapCommand.java:87)
        at org.springframework.aot.test.build.GenerateTestBootstrapCommand.call(GenerateTestBootstrapCommand.java:45)
        at picocli.CommandLine.executeUserObject(CommandLine.java:1953)
        at picocli.CommandLine.access$1300(CommandLine.java:145)
        at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2352)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2346)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2311)
        at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2179)
        at picocli.CommandLine.execute(CommandLine.java:2078)
        at org.springframework.aot.test.build.GenerateTestBootstrapCommand.main(GenerateTestBootstrapCommand.java:92)

> Task :generateTestAot FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':generateTestAot'.
> Process 'command '/usr/lib/jvm/java-11-openjdk-amd64/bin/java'' finished with non-zero exit value 1
...
BUILD FAILED in 39s

Project and Branch:
https://github.com/apereo/cas-overlay-template.git
origin/graal-starter

[hdeadman]

I made this PR to get past this issue: #1259