`NullPointerException` when ran with `-P`

It was reported that, given this invocation, script n. 1 failed with an exception. I don't have a reproducer at this time.

```bash
./01-validate-local-build-caching-same-location.sh -r file:///home/example/repo -b example-branch -g install -a -P\ lorem\,ipsum\,foo\,bar
```

```
[ERROR] Error executing a DevelocityListener callback
java.lang.NullPointerException: Cannot invoke "java.util.Collection.size()" because "c" is null
at java.util.LinkedHashSet. (LinkedHashSet.java:181)
at com.gradle.RootProjectExtractor.discoverAllProjects (RootProjectExtractor.java:61)
at com.gradle.RootProjectExtractor.extractRootProject (RootProjectExtractor.java:31)
at com.gradle.ConfigureDevelocityAdaptor.configure (ConfigureDevelocityAdaptor.java:48)
at com.gradle.ConfigureDevelocityListener.configure (ConfigureDevelocityListener.java:21)
at com.gradle.maven.internal.DevelocityLifecycleManager.a (SourceFile:400)
at java.lang.Iterable.forEach (Iterable.java:75)
at java.util.Collections$UnmodifiableCollection.forEach (Collections.java:1116)
at com.gradle.maven.internal.DevelocityLifecycleManager.b (SourceFile:398)
at com.gradle.maven.internal.DevelocityLifecycleManager.c (SourceFile:370)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept (ForEachOps.java:184)
at java.util.stream.ReferencePipeline$15$1.accept (ReferencePipeline.java:541)
at java.util.stream.IntPipeline$1$1.accept (IntPipeline.java:180)
at java.util.stream.Streams$RangeIntSpliterator.forEachRemaining (Streams.java:104)
at java.util.Spliterator$OfInt.forEachRemaining (Spliterator.java:712)
at java.util.stream.AbstractPipeline.copyInto (AbstractPipeline.java:509)
at java.util.stream.AbstractPipeline.wrapAndCopyInto (AbstractPipeline.java:499)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential (ForEachOps.java:151)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential (ForEachOps.java:174)
at java.util.stream.AbstractPipeline.evaluate (AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach (ReferencePipeline.java:596)
at com.gradle.maven.internal.DevelocityLifecycleManager.a (SourceFile:370)
at com.gradle.maven.internal.DevelocityLifecycleManager.onEvent (SourceFile:313)
at org.apache.maven.eventspy.internal.EventSpyDispatcher.onEvent (EventSpyDispatcher.java:86)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:908)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:283)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:206)
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:283)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:226)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:407)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:348)
```

Start with 01-validate-local-build-caching-same-location.sh and the reported invocation using -P, then inspect RootProjectExtractor.discoverAllProjects at the stack-trace location. A reproducer is not provided, so first establish the failure and its input conditions. Done means the invocation no longer raises the reported NullPointerException.

Written by the indexing model from the issue text.