rearranged _traverse to be easier to read

theano/gradient.py

@@ -213,9 +213,10 @@ def Rop(f, wrt, eval_points):
 
     def _traverse(node):
         """ TODO: writeme """
+
         if node is None:
-            return None
-        else:
+            return
+
         op = node.op
         inputs = node.inputs
 
@@ -273,7 +274,7 @@ def Rop(f, wrt, eval_points):
                 same_type_eval_points.append(y)
 
         seen_nodes[node] = op.R_op(node.inputs, same_type_eval_points)
-            return None
+    #end _traverse
 
     # Populate the dictionary
     for out in f: