Fix errors due to iterating over None-types in ivy resolve.
Review Request #3596 - Created March 22, 2016 and submitted
|nhoward_tw, stuhood, zundel|
IvyFetchResolveResult._jar_dependencies_for_target was returning None instead of an empty iterable, which was breaking the for-loop in IvyInfo.get_resolved_jars_for_coordinates. This makes _jar_dependencies_for_target return an empty tuple instead of None.
Manually confirmed that this fixes the problem in our internal repo.
CI confirmed that this didn't break any existing test-cases.
I haven't found a way to repro this in open-source yet (the artifact that was causing ivy to choke internally is an internal-only artifact that happens to be a tarball). I tried adding a test using an arbitrary tarball I found on maven central, but it didn't reproduce the original error.
CI passed here: https://travis-ci.org/pantsbuild/pants/builds/117770399