Got TypeError when running VGG example

[Auptla]

The error log is below:

TypeError                                 Traceback (most recent call last)
<ipython-input-15-73a1b345b022> in <module>()
----> 1 ig = integrated_gradients(model)

/home/ubuntu/GA/IntegratedGradients-master/IntegratedGradients.py in __init__(self, model, outchannels, verbose)
     73                 gradients = self.model.optimizer.get_gradients(self.model.output[:, c], self.model.input)
     74             if K.backend() == "theano":
---> 75                 gradients = self.model.optimizer.get_gradients(self.model.output[:, c].sum(), self.model.input)
     76 
     77             # Build computational graph that computes the tensors given inputs

/home/ubuntu/anaconda3/envs/theano_p27/lib/python2.7/site-packages/keras/optimizers.pyc in get_gradients(self, loss, params)
     88     def get_gradients(self, loss, params):
     89         grads = K.gradients(loss, params)
---> 90         if None in grads:
     91             raise ValueError('An operation has `None` for gradient. '
     92                              'Please make sure that all of your ops have a '

/home/ubuntu/anaconda3/envs/theano_p27/lib/python2.7/site-packages/theano/tensor/var.pyc in __iter__(self)
    630         except TypeError:
    631             # This prevents accidental iteration via builtin.sum(self)
--> 632             raise TypeError(('TensorType does not support iteration. '
    633                              'Maybe you are using builtin.sum instead of '
    634                              'theano.tensor.sum? (Maybe .max?)'))

TypeError: TensorType does not support iteration. Maybe you are using builtin.sum instead of theano.tensor.sum? (Maybe .max?)

[Auptla]

it only wrong with theano backend,
it works well with tensorflow backend