Apply workaround for http://goo.gl/bbtGg5.
diff --git a/src/pipeline/pipeline.py b/src/pipeline/pipeline.py
index 471f61e..01e84e4 100755
--- a/src/pipeline/pipeline.py
+++ b/src/pipeline/pipeline.py
@@ -1014,7 +1014,10 @@
     for name, module in module_dict.items():
       if name == '__main__':
         continue
-      found = getattr(module, cls.__name__, None)
+      try:
+        found = getattr(module, cls.__name__, None)
+      except ImportError:
+        pass
       if found is cls:
         break
     else: