Fixed minor bug.

theano/gof/fg.py

@@ -331,7 +331,7 @@ class FunctionGraph(utils.object2):
                             # if there is no path then r isn't really a graph input so we shouldn't be running error
                             # handler code in the first place
                             assert path is not None
-                            tr = getattr(r.tag, 'trace', None)
+                            tr = getattr(r.tag, 'trace', [])
                             detailed_err_msg = ""
                             if len(tr) > 0:
                                 detailed_err_msg += "\nBacktrace when the variable is created:\n"

theano/gof/link.py

@@ -157,7 +157,7 @@ def raise_with_op(node, thunk=None, exc_info=None, storage_map=None):
             " have the inputs shapes and strides printed.")
 
     # Print node backtraces
-    tr = getattr(node.outputs[0].tag, 'trace', None)
+    tr = getattr(node.outputs[0].tag, 'trace', [])
     if len(tr) > 0:
         detailed_err_msg += "\nBacktrace when the node is created:\n"
         

theano/gof/op.py

@@ -458,7 +458,7 @@ class PureOp(object):
                 detailed_err_msg = (
                     "For compute_test_value, one input test value does not"
                     " have the requested type.\n")
-                tr = getattr(v.tag, 'trace', None)
+                tr = getattr(v.tag, 'trace', [])
                 if len(tr) > 0:
                     detailed_err_msg += (
                         " \nBacktrace when that variable is created:\n")