We have a Maven project using the maven-source-plugin. When building the
project on Jenkins, it shows the following warning:

[INFO] *--- maven-jar-plugin:2.4:jar (default-jar) @ test-project ---
*[INFO] Building jar:
/home/jenkins/workspace/test-project/target/test-project-1.0.0-SNAPSHOT.jar[WARNING]
Failed to getClass for org.apache.maven.plugin.source.SourceJarMojo

I tested with maven-source-plugin 2.2.1, 2.3, and 2.4 and all of these
versions exhibit the same problem.

The problem does not appear if the project was compiled from NetBeans or command line.

(Initially, I thought this was a Maven issue, therefore I started a thread at the Maven user's mailing list:
http://maven-users.markmail.org/thread/jd74vnjnzfoef55e#query:+page:1+mid:no3jnbfgji2x63wj+state:results)