Hello,

I'm not sure if this is the correct place to leave a comment. If it is isn't, I apologize.

When instantiating autoencoder.DenoisingAutoencoder, the class requires a value associated with the variable 'act_dec'. If I'd like to specify a linear decoding function, then I must pass None using "Null" via yaml. However these lines throw an error since the yaml parser won't accept None as a dict keyword value. I expect there are other locations in pylearn2 where one would legitimately like to pass None via their yaml source.

--Andy