BUG: get_splits should return empty list, not empty dict

tests/test_data_portal.py

@@ -401,6 +401,10 @@ class DataPortalTestBase(WithDataPortal,
                          "Asset 10000 had a trade on fourth minute, so should "
                          "return that as the last trade on the fifth.")
 
+    def test_get_empty_splits(self):
+        splits = self.data_portal.get_splits([], self.trading_days[2])
+        self.assertEqual([], splits)
+
 
 class TestDataPortal(DataPortalTestBase):
     DATA_PORTAL_LAST_AVAILABLE_SESSION = None

zipline/data/data_portal.py

@@ -1139,7 +1139,7 @@ class DataPortal(object):
             List of splits, where each split is a (asset, ratio) tuple.
         """
         if self._adjustment_reader is None or not assets:
-            return {}
+            return []
 
         # convert dt to # of seconds since epoch, because that's what we use
         # in the adjustments db