JDK9 and maven-jar-plugin
The chances are mostly of an incompatible maven-plugin version in your module. You could try to update the plugin configuration in the parent module to the following and test:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>1.9</source>
<target>1.9</target>
<jdkToolchain>
<version>9</version>
</jdkToolchain>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
</plugin>
</plugins>
</build>
For the list of compatible versions of all the plugins, do refer to Maven#Java9+Jigsaw