Theano/Theano — pull request #1296 by pascanur (2013-03-21 15:54:16+00:00)
Title: fix bug reported by Nicolas

The problem was that the new version of compute_gradient does not return None for a disconnected gradient anymore, but it raises a DisconnectedError. I've changed the code to catch that error and replace it with None, so the rest of the logic in scan_op.grad works as it used to.

I've added a test (the sample send by Nicolas).