Javadoc warnings on travis, none on local gradle runs

I wanted to clean up old javadoc warnings on a project and succeeded locally: when running ./gradlew assembly, no warnings are emitted.

However, javadoc creation on travis seems to be much stricter as the build fails with several warnings. Both builds (travis and local) use the same Java version. It seems to me that travis injects some hidden configuration but I was unable to find out anything about it.

I would in fact prefer the “normal” gradle build to behave as the travis one does as it generates sensible additional warnings. Does anybody have any pointers on how to make both builds behave the same?