Hey Beam, I'm attempting to patch beam (PR here: https://github.com/apache/beam/pull/3933) but am running into a warning that I can't figure out the cause to. The warning is "bootstrap class path not set in conjunction with -source 1.7" which, after some googling, seems like it's an issue with building sources to target one java version while using backwards incompatible features? I might be misunderstanding though. Weirdly, "mvn clean verify" succeeds locally.
Posting here to see if anyone's run into this, or knows of a possible solution. Full build context here: https://builds.apache.org/job/beam_PreCommit_Java_MavenInstall/14761/org.apache.beam$beam-sdks-java-io-google-cloud-platform/console
