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