NullPointerException from ClassWrangler.getGroovyVersionString

[jglick]

Unable to get Groovy version from GroovySystem, trying InvokerHelper.
[WARN] Unable to get Groovy version from InvokerHelper or GroovySystem, trying jar name.
Unable to determine Groovy version. Is Groovy declared as a dependency?
…
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.gmavenplus:gmavenplus-plugin:1.13.1:execute (…) on project …: Execution … of goal org.codehaus.gmavenplus:gmavenplus-plugin:1.13.1:execute failed.
	at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute(MojoExecutor.java:274)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:196)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:160)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
	at org.mvndaemon.mvnd.builder.SmartBuilderImpl.buildProject(SmartBuilderImpl.java:178)
	at org.mvndaemon.mvnd.builder.SmartBuilderImpl$ProjectBuildTask.run(SmartBuilderImpl.java:198)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution … of goal org.codehaus.gmavenplus:gmavenplus-plugin:1.13.1:execute failed.
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:148)
	at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute(MojoExecutor.java:271)
	... 11 common frames omitted
Caused by: java.lang.NullPointerException: null
	at org.codehaus.gmavenplus.util.ClassWrangler.getGroovyVersionString(ClassWrangler.java:121)
	at org.codehaus.gmavenplus.util.ClassWrangler.logGroovyVersion(ClassWrangler.java:224)
	at org.codehaus.gmavenplus.mojo.ExecuteMojo.doExecute(ExecuteMojo.java:118)
	at org.codehaus.gmavenplus.mojo.ExecuteMojo.execute(ExecuteMojo.java:90)
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
	... 12 common frames omitted

GMavenPlus/src/main/java/org/codehaus/gmavenplus/util/ClassWrangler.java

Line 121 in eb7f459

int newIdx = jar.indexOf("-" + i);

seems to fail to account for a null return value from getGroovyJar.

[keeganwitt]

Usually this happens because you don't have groovy as a project dependency. Can I see your POM?

[jglick]

Oh I long since solved the root problem—had an improper dependency somewhere. The point of the issue is that the mojo is throwing an NPE rather than gracefully reporting an error in this corner case. Or rather, it does log appropriate errors, but the immediate build failure cause is an NPE which grabs attention away from them.

[keeganwitt]

I think that stacktrace only shows up when you are using a commandline switch such as debug (-X). But you're right, the message could be cleaned up.

[jglick]

a commandline switch such as debug (-X)

-e rather. If you do not, it is worse: you see that the mojo failed but you only see that there is a NullPointerException with no idea why.