Merge pull request #822 from tacaswell/fix/v1_rootmap

FIX: return and empty dict for type stability

databroker/v1.py

@@ -67,6 +67,7 @@ def root_map(self):
             "details are handled for you on the server side, so you should not worry "
             "about this message unless you encounter trouble loading large array data."
         )
+        return {}
 
     def register_handler(self, *args, **kwargs):
         warnings.warn(