Fix config override in import_from_tsv

Summary:
This was broken because `override_config_dict` cannot handle a `None` override.

Issue introduced in af783df (a.k.a., D16600944).

Fixes facebookresearch#93.

Reviewed By: adamlerer

Differential Revision: D16936289

fbshipit-source-id: 721727a97c4ee76105298e47610db11c5cf0c3e7

torchbiggraph/converters/import_from_tsv.py

@@ -381,9 +381,7 @@ def main():
 
     if opt.param is not None:
         overrides = chain.from_iterable(opt.param)  # flatten
-    else:
-        overrides = None
-    config_dict = override_config_dict(config_dict, overrides)
+        config_dict = override_config_dict(config_dict, overrides)
 
     entity_configs, relation_configs, entity_path, dynamic_relations = \
         parse_config_partial(config_dict)