NPE when running shamrock:create in existing Maven project

[gsmet]

I accidentally run mvn -X org.jboss.shamrock:shamrock-maven-plugin:1.0.0.Alpha1-SNAPSHOT:create -DprojectGroupId=org.acme -DprojectArtifactId=using-opentracing -DclassName="org.acme.opentracing.TracedResource" -Dpath="/hello" -Dextensions="tracing" in the root of my Shamrock git clone.

I end up with a weird state:

• a src/ directory created at the root
• a NPE:

Caused by: java.lang.NullPointerException
    at org.jboss.shamrock.maven.CreateProjectMojo.addPluginManagementSection (CreateProjectMojo.java:218)
    at org.jboss.shamrock.maven.CreateProjectMojo.addMainPluginConfig (CreateProjectMojo.java:186)
    at org.jboss.shamrock.maven.CreateProjectMojo.execute (CreateProjectMojo.java:136)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:208)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:954)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:192)
    at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:356)

While it's a user error, I thought it was supposed to create a subdirectory if the directory was not empty? Moreover failing with a NPE does not look nice.

I wouldn't mind if we threw an error altogether if we try to do that in an existing Maven project.

[cescoffier]

good catch! Right now it tries to make a guess if you want to create or extend. It should be improved and not failed with an NPE.

[cescoffier]

typically, if there is a pom.xml using packaging pom - it should report a user error.

[gsmet]

Hmmm, I'm not sure we should try to extend an existing project with a create operation. I would simplify that.

[cescoffier]

Yes, that would simplify a LOT! so +1.
However, add-extension will still need to do some lookup, but it's much simpler in this case.