NPE during compile

I have a new Scala module as part of a multi-module project. When attempting to compile with the new module, I get the following error:

$ mvn -T C1 -e clean package
...
[ERROR] Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile (default) on project batch-spark: Execution default of goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile failed.: NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile (default) on project batch-spark: Execution default of goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile failed.
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:213)
        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.builder.multithreaded.MultiThreadedBuilder$1.call(MultiThreadedBuilder.java:200)
        at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call(MultiThreadedBuilder.java:196)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default of goal net.alchim31.maven:scala-maven-plugin:3.3.1:compile failed.
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:145)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        ... 11 more
Caused by: java.lang.NullPointerException
        at scala_maven.FileUtils.pathOf(FileUtils.java:12)
        at scala_maven.ScalaMojoSupport.addCompilerToClasspath(ScalaMojoSupport.java:559)
        at scala_maven.ScalaMojoSupport.getToolClasspath(ScalaMojoSupport.java:825)
        at scala_maven.ScalaMojoSupport.getEmptyScalaCommand(ScalaMojoSupport.java:797)
        at scala_maven.ScalaMojoSupport.getScalaCommand(ScalaMojoSupport.java:753)
        at scala_maven.ScalaMojoSupport.getScalaCommand(ScalaMojoSupport.java:732)
        at scala_maven.ScalaCompilerSupport.compile(ScalaCompilerSupport.java:153)
        at scala_maven.ScalaCompilerSupport.doExecute(ScalaCompilerSupport.java:99)
        at scala_maven.ScalaMojoSupport.execute(ScalaMojoSupport.java:584)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
        ... 12 more
[ERROR] 
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException
[ERROR] 
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :batch-spark

The batch-spark submodule’s pom.xml contains the plugin:

        <sourceDirectory>src/main/scala</sourceDirectory>

        <plugins>
            <plugin>
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.3.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>testCompile</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <scalaVersion>${scala.version}</scalaVersion>
                </configuration>
            </plugin>
        </plugins>
    </build>

Any recommendations on how to fix this?

[andreak]

Jep, removing <recompileMode>incremental</recompileMode> fixed it. Any news about if this will be fixed?

[davidB]

incremental support for java 9, will not be done.

The new zinc compiler will not be integrated in this plugin (until PR) And maybe to avoid this kind of issue in future version, the incremetal compiler option will be removed (or disabled for scala version > 2.12 or java version > 8)

You can take a look at https://github.com/random-maven/scalor-maven-plugin (works with zinc 1.x)