<!-- JDK 9 minimal source and target versions are 1.6 -->
                <jdkVersion>1.6</jdkVersion>
            </properties>
            <build>
                <plugins>
                    <plugin>
                        <artifactId>maven-javadoc-plugin</artifactId>
                        <configuration>
                            <source>1.6</source>
                        </configuration>