pants: Flaky product graph construction: Invalid requirement, parse error at "u''"

https://api.travis-ci.org/v3/job/463150773/log.txt

travis_fold:start:BackendTests
[=== 05:35 Running internal backend python tests ===]
timestamp: 2018-12-04T04:51:24.356140
Exception caught: (pants.build_graph.address_lookup_error.AddressLookupError)
  File ".bootstrap/_pex/pex.py", line 349, in execute
    exit_code = self._wrap_coverage(self._wrap_profiling, self._execute)
  File ".bootstrap/_pex/pex.py", line 281, in _wrap_coverage
    return runner(*args)
  File ".bootstrap/_pex/pex.py", line 312, in _wrap_profiling
    return runner(*args)
  File ".bootstrap/_pex/pex.py", line 394, in _execute
    return self.execute_entry(self._pex_info.entry_point)
  File ".bootstrap/_pex/pex.py", line 506, in execute_entry
    return runner(entry_point)
  File ".bootstrap/_pex/pex.py", line 528, in execute_pkg_resources
    return runner()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/pants_loader.py", line 71, in main
    PantsLoader.run()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/pants_loader.py", line 67, in run
    cls.load_and_execute(entrypoint)
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/pants_loader.py", line 60, in load_and_execute
    entrypoint_main()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/pants_exe.py", line 39, in main
    PantsRunner(exiter, start_time=start_time).run()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/pants_runner.py", line 62, in run
    return runner.run()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/local_pants_runner.py", line 159, in run
    self._run()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/local_pants_runner.py", line 227, in _run
    goal_runner_result = self._maybe_run_v1(run_tracker, reporting)
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/local_pants_runner.py", line 176, in _maybe_run_v1
    return goal_runner_factory.create().run()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/goal_runner.py", line 125, in create
    goals, context = self._setup_context()
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/bin/goal_runner.py", line 95, in _setup_context
    self._root_dir
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/init/engine_initializer.py", line 226, in create_build_graph
    for _ in graph.inject_roots_closure(target_roots):
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/legacy/graph.py", line 217, in inject_roots_closure
    for address in self._inject_specs(target_roots.specs):
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/legacy/graph.py", line 270, in _inject_specs
    subjects)
  File "/opt/pyenv/versions/2.7.14/lib/python2.7/contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/legacy/graph.py", line 237, in _resolve_context
    'Build graph construction failed: {} {}'.format(type(e).__name__, str(e))

Exception message: Build graph construction failed: ExecutionError 1 Exception encountered:
Computing Select(Specs(dependencies<=tuple>=(DescendantAddresses(directory=u'pants-plugins/tests/python'),), matcher<=SpecsMatcher>=SpecsMatcher(tags<=tuple>=(), exclude_patterns<=tuple>=())), =TransitiveHydratedTargets)
  Computing Task(transitive_hydrated_targets, Specs(dependencies<=tuple>=(DescendantAddresses(directory=u'pants-plugins/tests/python'),), matcher<=SpecsMatcher>=SpecsMatcher(tags<=tuple>=(), exclude_patterns<=tuple>=())), =TransitiveHydratedTargets, true)
    Computing Task(transitive_hydrated_target, pants-plugins/tests/python/internal_backend_test/sitegen:sitegen, =TransitiveHydratedTarget, true)
      Computing Task(transitive_hydrated_target, 3rdparty/python:future, =TransitiveHydratedTarget, true)
        Computing Task(hydrate_target, 3rdparty/python:future, =HydratedTarget, true)
          Computing Task(hydrate_struct, 3rdparty/python:future, =(symbol table types), true)
            Computing Task(resolve_unhydrated_struct, 3rdparty/python:future, =UnhydratedStruct, true)
              Computing Task(parse_address_family, Dir(path=3rdparty/python), =AddressFamily, true)
                Throw(Failed to parse 3rdparty/python/BUILD:
Invalid requirement, parse error at "u''")
                  Traceback (most recent call last):
                    File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/native.py", line 523, in extern_generator_send
                      res = c.from_value(func[0]).send(c.from_value(arg[0]))
                    File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/build_files.py", line 61, in parse_address_family
                      address_mapper.parser))
                    File "/home/travis/.pex/code/65c2938b2de17351c60a770eb88d6bc1f1272701/pants/engine/mapper.py", line 55, in parse
                      raise MappingError('Failed to parse {}:\n{}'.format(filepath, e))
                  MappingError: Failed to parse 3rdparty/python/BUILD:
                  Invalid requirement, parse error at "u''"