Add JAVA_HOME location to maven-javadoc-plugin configuration.

Solution from this StackOverflow question

Error for command

$ mvn verify sonar:sonar

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.1.1:jar (attach-javadoc) on project dummy4j: MavenReportException:
Error while generating Javadoc: Unable to find javadoc command: The environment variable JAVA_HOME is not correctly set.

For more information read the following articles: http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

My environment details:

$ javac --version
javac 11.0.8

$ mvn --version
Apache Maven 3.6.0
Maven home: /usr/share/maven
Java version: 11.0.8, vendor: Ubuntu, runtime: /usr/lib/jvm/java-11-openjdk-amd64

$ which java
/usr/bin/java

$ dirname $(dirname $(readlink -f $(which javac)))
/usr/lib/jvm/java-11-openjdk-amd64

Empty result for:

$ echo $JAVA_HOME

daniel-frak / dummy4j

Add JAVA_HOME location to maven-javadoc-plugin configuration. #16