[plugin-maven] BUG: `GoogleJavaFormatStep.defaultVersion` throws NPE in CI Java matrix

In the context of a GitHub Actions workflow, upgrading my Maven toolchain from single JDK to [Java matrix](https://github.com/actions/setup-java?tab=readme-ov-file#testing-against-different-java-versions), I'm experiencing what seems to be a bug affecting Spotless Maven plugin (version 3.0.0):
- in **simple setup (just JDK 11)**, Spotless Maven plugin works perfectly fine :sunglasses: — see [workflow execution summary](https://github.com/pdfclown/pdfclown-common/actions/runs/19529834372/job/55909989485)
- in **Java matrix (JDK 11, 21, 25)**, weirdly enough, *with the same JDK 11 Spotless fails* :astonished: (see stacktrace at the bottom), *whilst with JDK 21 and 25 it works perfectly fine* :confounded: — see [workflow execution summary](https://github.com/pdfclown/pdfclown-common/actions/runs/19554560715/job/55993941771)

So, recapping: with JDK 11, Spotless works perfectly fine in simple setup, but fails within Java matrix; on the contrary, with other JDKs after the first one, it works perfectly fine within Java matrix.

The error is *deterministically reproducible* (even locally via [nektos/act](https://github.com/nektos/act)) *and affects both `check` and `apply` goals identically*. It originates in [Jvm.getRecommendedFormatterVersion()](https://github.com/diffplug/spotless/blob/ed43dc202a2b5d009981314a81491d77c4c46465/lib/src/main/java/com/diffplug/spotless/Jvm.java#L123):

```java
@Nullable public V getRecommendedFormatterVersion() {
Integer configuredJvmVersionOrNull = jvm2fmtMaxVersion.floorKey(Jvm.version());
return configuredJvmVersionOrNull == null ? null : jvm2fmtMaxVersion.get(configuredJvmVersionOrNull);
}
```
Apparently, either `Jvm.version()` is undefined, or `jvm2fmtMaxVersion` misses matching floor key — there must be some condition going unexpected during the initialization of Spotless... The fact it affects JDK 11 only in Java matrix, whilst the parallel execution of other JDKs is always successful, is pretty strange... 🤔

Stacktrace:
```
Error: Failed to execute goal com.diffplug.spotless:spotless-maven-plugin:3.0.0:check (default) on project pdfclown-common-super: Execution default of goal com.diffplug.spotless:spotless-maven-plugin:3.0.0:check failed. NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.diffplug.spotless:spotless-maven-plugin:3.0.0:check (default) on project pdfclown-common-super: Execution default of goal com.diffplug.spotless:spotless-maven-plugin:3.0.0:check failed.
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:333)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:316)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:174)
at org.apache.maven.lifecycle.internal.MojoExecutor.access$000 (MojoExecutor.java:75)
at org.apache.maven.lifecycle.internal.MojoExecutor$1.run (MojoExecutor.java:162)
at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute (DefaultMojosExecutionStrategy.java:39)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:159)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:105)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:73)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:53)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:118)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:261)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:173)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:101)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:906)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:283)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:206)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:569)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:255)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:201)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:361)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:314)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default of goal com.diffplug.spotless:spotless-maven-plugin:3.0.0:check failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:133)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:328)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:316)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:174)
at org.apache.maven.lifecycle.internal.MojoExecutor.access$000 (MojoExecutor.java:75)
at org.apache.maven.lifecycle.internal.MojoExecutor$1.run (MojoExecutor.java:162)
at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute (DefaultMojosExecutionStrategy.java:39)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:159)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:105)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:73)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:53)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:118)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:261)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:173)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:101)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:906)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:283)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:206)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:569)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:255)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:201)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:361)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:314)
Caused by: java.lang.NullPointerException
at java.util.Objects.requireNonNull (Objects.java:209)
at com.diffplug.spotless.java.GoogleJavaFormatStep.defaultVersion (GoogleJavaFormatStep.java:134)
at com.diffplug.spotless.java.GoogleJavaFormatStep.createRemoveUnusedImportsOnly (GoogleJavaFormatStep.java:96)
at com.diffplug.spotless.java.RemoveUnusedImportsStep.create (RemoveUnusedImportsStep.java:54)
at com.diffplug.spotless.maven.java.RemoveUnusedImports.newFormatterStep (RemoveUnusedImports.java:32)
at com.diffplug.spotless.maven.FormatterFactory.lambda$newFormatter$0 (FormatterFactory.java:98)
at java.util.stream.ReferencePipeline$3$1.accept (ReferencePipeline.java:197)
at java.util.stream.ReferencePipeline$2$1.accept (ReferencePipeline.java:179)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining (ArrayList.java:1625)
at java.util.stream.AbstractPipeline.copyInto (AbstractPipeline.java:509)
at java.util.stream.AbstractPipeline.wrapAndCopyInto (AbstractPipeline.java:499)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential (ReduceOps.java:921)
at java.util.stream.AbstractPipeline.evaluate (AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect (ReferencePipeline.java:682)
at com.diffplug.spotless.maven.FormatterFactory.newFormatter (FormatterFactory.java:99)
at com.diffplug.spotless.maven.FormattersHolder.create (FormattersHolder.java:46)
at com.diffplug.spotless.maven.AbstractSpotlessMojo.execute (AbstractSpotlessMojo.java:269)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:126)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:328)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:316)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:174)
at org.apache.maven.lifecycle.internal.MojoExecutor.access$000 (MojoExecutor.java:75)
at org.apache.maven.lifecycle.internal.MojoExecutor$1.run (MojoExecutor.java:162)
at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute (DefaultMojosExecutionStrategy.java:39)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:159)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:105)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:73)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:53)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:118)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:261)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:173)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:101)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:906)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:283)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:206)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:569)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:255)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:201)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:361)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:314)
```

Reproduce el fallo del plugin de Maven con la matriz indicada de Java 11, 21 y 25, incluidos los objetivos check y apply. Empieza por Jvm.java en getRecommendedFormatterVersion(), y después sigue GoogleJavaFormatStep.defaultVersion() y la ruta de RemoveUnusedImports mostrada en el stack trace. Se considera terminado cuando la matriz ya no lanza NullPointerException y los objetivos afectados se completan correctamente.

Escrito por el modelo de indexación a partir del texto del issue.