fix bug where flatten() excluded the option

random_sets/datasources.py

@@ -122,9 +122,9 @@ class DataSource:
         """
 
         # If there is no data for the specified option, stop now.
-        flattened = []
+        flattened = [option]
         if not self.data[option]:
-            return [option]
+            flattened
 
         if hasattr(self.data[option], 'keys'):
             # if the option is a dict, we assume the values are lists; we select a random item