artifacts: allow missing tarball in BundleTastFiles

Now that recipes always attempts to upload artifacts, missing TastFiles
are less of an issue.

BUG=chromium:1086630
TEST=unit tests pass

Change-Id: I3ad0c8e33c426e4446ddc2dc92a22fd394a38519
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2241735
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
Tested-by: LaMont Jones <lamontjones@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
diff --git a/api/controller/artifacts_unittest.py b/api/controller/artifacts_unittest.py
index e231870..1d6267f 100644
--- a/api/controller/artifacts_unittest.py
+++ b/api/controller/artifacts_unittest.py
@@ -309,12 +309,12 @@
                      os.path.join(self.output_dir, 'tast_bundles.tar.gz'))
 
   def testBundleTastFilesNoLogs(self):
-    """BundleTasteFiles dies when no tast files found."""
+    """BundleTasteFiles succeeds when no tast files found."""
     self.PatchObject(commands, 'BuildTastBundleTarball',
                      return_value=None)
-    with self.assertRaises(cros_build_lib.DieSystemExit):
-      artifacts.BundleTastFiles(self.target_request, self.response,
-                                self.api_config)
+    artifacts.BundleTastFiles(self.target_request, self.response,
+                              self.api_config)
+    self.assertEqual(list(self.response.artifacts), [])
 
   def testBundleTastFilesLegacy(self):
     """BundleTastFiles handles legacy args correctly."""