Merge pull request dart-lang/package_config#51 from srawlins/missing-return

Fix missing_return violation newly enforced in Dart ~2.3.2-dev.0.1

pkgs/package_config/test/discovery_analysis_test.dart

diff --git a/pkgs/package_config/test/discovery_analysis_test.dart b/pkgs/package_config/test/discovery_analysis_test.dart
index c819a90..e432454 100644
--- a/pkgs/package_config/test/discovery_analysis_test.dart
+++ b/pkgs/package_config/test/discovery_analysis_test.dart
@@ -41,6 +41,7 @@
     var map = ctx.asMap();
     expect(map.keys.map((dir) => dir.path),
         unorderedEquals([directory.path, fooDir.path, barDir.path]));
+    return null;
   });
 }