mvn exec:java fails

[INFO] Reactor Summary for Quickstart: jaxrs-jwt 20.0.0.Final:
[INFO]
[INFO] Quickstart: jaxrs-jwt .............................. FAILURE [ 0.361 s]
[INFO] Quickstart: jaxrs-jwt - client ..................... SKIPPED
[INFO] Quickstart: jaxrs-jwt - service .................... SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.056 s
[INFO] Finished at: 2020-06-27T13:39:17+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.6.0:java (default-cli) on project jaxrs-jwt: The parameters 'mainClass' for goal org.codehaus.mojo:exec-maven-plugin:1.6.0:java are missing or invalid -> [Help 1]
[ERROR]

mvn -v
Apache Maven 3.6.3
Maven home: /usr/share/maven
Java version: 14.0.1, vendor: Private Build, runtime: /usr/lib/jvm/java-14-openjdk-amd64
Default locale: de_DE, platform encoding: UTF-8
OS name: "linux", version: "5.4.0-39-generic", arch: "amd64", family: "unix"

Executing the clent directly via:
$JAVA_HOME/bin/java -classpath $CLASSPATH org.jboss.quickstarts.jaxrsjwt.client.JwtRestClient

Euns successfully indeed. So this seems to be an issue with the pom.xml