Start from a totally clean environment (eg. a clean VM if you can), clone everything.

Comment out the existing fluent module from the pom.xml

...
<!--
  <module>fluent</module>
  <module>spring</module>
  <module>e2e</module>
  <module>examples</module>
-->
...

mvn install

cd fluent-gen; ./generate.sh

Comment the above modules back into the pom.xml

mvn install