[MNG-8507] NPE when running openrewrite

**[Guillaume Nodet](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=gnt)** opened **[MNG-8507](https://issues.apache.org/jira/browse/MNG-8507?redirect=false)** and commented

The openrewrite plugin throws a NPE:

```
[WARNING] Unable to parse checkstyle configuration. Checkstyle will not inform rewrite execution.
java.lang.NullPointerException: Cannot invoke "org.apache.maven.model.InputLocation.getSource()" because the return value of "org.apache.maven.model.Plugin.getLocation(Object)" is null
at org.openrewrite.maven.ConfigurableRewriteMojo.loadStyles(ConfigurableRewriteMojo.java:262)
at org.openrewrite.maven.AbstractRewriteBaseRunMojo.loadSourceSet(AbstractRewriteBaseRunMojo.java:231)
at org.openrewrite.maven.AbstractRewriteBaseRunMojo.listResults(AbstractRewriteBaseRunMojo.java:152)
at org.openrewrite.maven.AbstractRewriteRunMojo.execute(AbstractRewriteRunMojo.java:64)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:144)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2(MojoExecutor.java:339)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute(MojoExecutor.java:310)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:214)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:179)
at org.apache.maven.lifecycle.internal.MojoExecutor$1.run(MojoExecutor.java:168)
at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute(DefaultMojosExecutionStrategy.java:39)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:165)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:110)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:76)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:60)
at org.apache.maven.lifecycle.internal.DefaultLifecycleStarter.execute(DefaultLifecycleStarter.java:123)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:311)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:225)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:149)
at org.apache.maven.cling.invoker.mvn.MavenInvoker.doExecute(MavenInvoker.java:470)
at org.apache.maven.cling.invoker.mvn.MavenInvoker.execute(MavenInvoker.java:95)
at org.apache.maven.cling.invoker.mvn.MavenInvoker.execute(MavenInvoker.java:85)
at org.apache.maven.cling.invoker.LookupInvoker.doInvoke(LookupInvoker.java:145)
at org.apache.maven.cling.invoker.LookupInvoker.invoke(LookupInvoker.java:116)
at org.apache.maven.cling.ClingSupport.run(ClingSupport.java:64)
at org.apache.maven.cling.MavenCling.main(MavenCling.java:51)
at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.lang.reflect.Method.invoke(Method.java:580)
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)
```

---

**Affects:** 4.0.0-rc-2

Start with ConfigurableRewriteMojo.java at ConfigurableRewriteMojo.loadStyles, the first project entry point named in the stack trace. Run the openrewrite plugin scenario that produces the reported failure and verify that loading styles completes without the NullPointerException.

Written by the indexing model from the issue text.